Logging format 'text' considered invalid

When using logging format `text` for `gitaly` chart it's considered `invalid`.
In documentation `format` value of `[logging]` section should accept: `json` or `text`

![image](/uploads/457e603e92498e00f4d61496126e8567/image.png)

Gitaly pod logs:
```
root@ip-10-2-4-231:~# kubectl logs -n gitlab gitlab-gitaly-0
+ /scripts/set-config /etc/gitaly/templates /etc/gitaly
Begin parsing .erb files from /etc/gitaly/templates
Writing /etc/gitaly/config.toml
Copying other config files found in /etc/gitaly/templates
+ exec /bin/sh -c '"/scripts/process-wrapper"'
Starting Gitaly

*** /var/log/gitaly/gitaly.log ***
time="2020-11-11T19:06:22Z" level=info msg="Starting Gitaly" version="Gitaly, version 13.5.3"
time="2020-11-11T19:06:22Z" level=warning msg="git path not configured. Using default path resolution" resolvedPath=/usr/local/bin/git
time="2020-11-11T19:06:22Z" level=info msg="clearing disk cache object folder" path=/home/git/repositories
time="2020-11-11T19:06:22Z" level=info msg="moving disk cache object folder to /home/git/repositories/+gitaly/tmp/diskcache085180550" path=/home/git/repositories
time="2020-11-11T19:06:22Z" level=info msg="disk cache object folder doesn't exist, no need to remove" path=/home/git/repositories
time="2020-11-11T19:06:22Z" level=info msg="Starting file walker for /home/git/repositories/+gitaly/cache" path=/home/git/repositories/+gitaly/cache
time="2020-11-11T19:06:22Z" level=info msg="Starting file walker for /home/git/repositories/+gitaly/state" path=/home/git/repositories/+gitaly/state
time="2020-11-11T19:06:22Z" level=info msg="cleared all cache object files in /home/git/repositories/+gitaly/tmp/diskcache085180550 after 4.352483ms" path=/home/git/repositories
time="2020-11-11T19:06:23Z" level=fatal msg="invalid logger format" format=text
```

Logging section for the `gitaly` ConfigMap using `text` as format:
```
root@ip-10-2-4-231:~# kubectl get cm -n gitlab gitlab-gitaly -o yaml | grep 'logging' -A5
    [logging]
    format = "text"
    dir = "/var/log/gitaly"

    [auth]
    token = "<%= File.read('/etc/gitlab-secrets/gitaly/gitaly_token').strip.dump[1..-2] %>"
```

---

### Normal behavior

The working logging section for the `gitaly` ConfigMap with `json` value:
```
root@ip-10-2-4-231:~# kubectl get cm -n gitlab gitlab-gitaly -o yaml | grep 'logging' -A5
    [logging]
    format = "json"
    dir = "/var/log/gitaly"

    [auth]
    token = "<%= File.read('/etc/gitlab-secrets/gitaly/gitaly_token').strip.dump[1..-2] %>"
```

Gitaly log when using `json` as `[logging]` value for the `format`:
```
root@ip-10-2-4-231:~# kubectl logs -n gitlab gitlab-gitaly-0
+ /scripts/set-config /etc/gitaly/templates /etc/gitaly
Begin parsing .erb files from /etc/gitaly/templates
Writing /etc/gitaly/config.toml
Copying other config files found in /etc/gitaly/templates
+ exec /bin/sh -c '"/scripts/process-wrapper"'
Starting Gitaly

*** /var/log/gitaly/gitaly.log ***
time="2020-11-11T19:27:11Z" level=info msg="Starting Gitaly" version="Gitaly, version 13.5.3"
time="2020-11-11T19:27:11Z" level=warning msg="git path not configured. Using default path resolution" resolvedPath=/usr/local/bin/git
time="2020-11-11T19:27:11Z" level=info msg="clearing disk cache object folder" path=/home/git/repositories
time="2020-11-11T19:27:11Z" level=info msg="moving disk cache object folder to /home/git/repositories/+gitaly/tmp/diskcache451226427" path=/home/git/repositories
time="2020-11-11T19:27:11Z" level=info msg="disk cache object folder doesn't exist, no need to remove" path=/home/git/repositories
time="2020-11-11T19:27:11Z" level=info msg="Starting file walker for /home/git/repositories/+gitaly/cache" path=/home/git/repositories/+gitaly/cache
time="2020-11-11T19:27:11Z" level=info msg="Starting file walker for /home/git/repositories/+gitaly/state" path=/home/git/repositories/+gitaly/state
time="2020-11-11T19:27:11Z" level=info msg="cleared all cache object files in /home/git/repositories/+gitaly/tmp/diskcache451226427 after 4.46173ms" path=/home/git/repositories
{"address":"/home/git/internal.sock","level":"info","msg":"listening at unix address","time":"2020-11-11T19:27:12.101Z"}
{"address":"0.0.0.0:8075","level":"info","msg":"listening at tcp address","time":"2020-11-11T19:27:12.101Z"}
{"address":":9236","level":"info","msg":"starting prometheus listener","time":"2020-11-11T19:27:12.105Z"}
{"level":"info","msg":"finished tempdir cleaner walk","storage":"default","time":"2020-11-11T19:27:12.105Z","time_ms":6}
{"level":"info","msg":"starting RSS monitor","supervisor.name":"gitaly-ruby.1","supervisor.rss_threshold":209715200,"time":"2020-11-11T19:27:12.106Z"}
{"level":"info","msg":"starting RSS monitor","supervisor.name":"gitaly-ruby.0","supervisor.rss_threshold":209715200,"time":"2020-11-11T19:27:12.106Z"}
{"level":"warning","msg":"spawned","supervisor.args":["bundle","exec","bin/ruby-cd","/","/srv/gitaly-ruby/bin/gitaly-ruby","10","/home/git/ruby.1"],"supervisor.name":"gitaly-ruby.1","supervisor.pid":25,"time":"2020-11-11T19:27:12.107Z"}
{"level":"warning","msg":"spawned","supervisor.args":["bundle","exec","bin/ruby-cd","/","/srv/gitaly-ruby/bin/gitaly-ruby","10","/home/git/ruby.0"],"supervisor.name":"gitaly-ruby.0","supervisor.pid":26,"time":"2020-11-11T19:27:12.108Z"}
{"level":"info","msg":"PID 26 BUNDLE_GEMFILE=/srv/gitaly-ruby/Gemfile","supervisor.args":["bundle","exec","bin/ruby-cd","/","/srv/gitaly-ruby/bin/gitaly-ruby","10","/home/git/ruby.0"],"supervisor.name":"gitaly-ruby.0","time":"2020-11-11T19:27:12.552Z"}
{"level":"info","msg":"PID 25 BUNDLE_GEMFILE=/srv/gitaly-ruby/Gemfile","supervisor.args":["bundle","exec","bin/ruby-cd","/","/srv/gitaly-ruby/bin/gitaly-ruby","10","/home/git/ruby.1"],"supervisor.name":"gitaly-ruby.1","time":"2020-11-11T19:27:12.576Z"}
```

### Version details

Kubernetes, version 1.16  
Gitaly, version 13.5.3  
GitLab, version 13.5.3  
GitLab Cloud Native Helm chart, version 4.5.3

Story points: 2.0