Fixes #1288450 - Adds confirmation dialogue to config file upload in the service inspector

### Notes
Create a config.yaml file with the following contents:
```
ceph:
  auth-supported: "foo"
```
### To QA
__Ghost Inspector__
- Drag and drop `ceph` from the charm browser
- Click the config file upload button and select the `config.yaml` file.
- The config options should disappear.
- Click to remove the file
- The config options should reappear.
- Click the config file upload button and select the `config.yaml` file.
- Deploy the charm.
- Change to the `settings` tab and the `auth-supported` value should read `foo`.

__Service Inspector__
- Deploy ceph
- Click the `settings` tab and then click to upload the `config.yaml` file.
- The config options should disappear.
- Click to remove the file
- The config options should reappear.
- Click the config file upload button and select the `config.yaml` file.
- Click `save changes`.
- The `auth-supported` value should now read `foo`.