Add documentation
Remove template parameter

I think this is leftover from when we changed the nginx module.

See ac5714d8.
Validate parameters

It’s a good idea, and leads to easier maintenance in the future.
Generate Request-Id header for spotlight

The networking is…interesting. We have:

```
GET /performance
Host www.gov.uk
```

over the public internet goes through CDN to GOV.UK origin servers.

Here it hits the [router](https://github.com/alphagov/router).

The router looks up data in the [router-api](https://github.com/alphagov/router-api) to decide
which backend handles that request. Currently this is the spotlight
backend. It then goes via a local dnsmasq | /etc/hosts lookup to the
GOV.UK frontend loadbalancer, where it is then proxied via ngxinx to
the Performance Platform environment.
Merge pull request #600 from alphagov/feature/spotlight-request-id

Generate Request-Id header for spotlight
Add nginx rate-limiting configuration
Merge pull request #601 from alphagov/feature/nginx-rate-limiting

Add nginx rate-limiting configuration
Add mongodb collectd plugin

We have some concerns around mongodb performance in certain situations.
This should give us better visibility of their magnitude.
Merge pull request #602 from alphagov/add-collectd-mongodb

Add mongodb collectd plugin
Create a user for upcoming ITHC usage
Merge pull request #603 from alphagov/feature/ithc-configuration

Create a user for upcoming ITHC usage
Include collectd before adding mongo collectd

Because we're using variables from $::collectd::params we need to
include collectd first.
Fix typo on new user config
Merge pull request #605 from alphagov/fix-typo-in-user

Fix typo on new user config
Merge pull request #604 from alphagov/fix-mongo-collectd

Include collectd before adding mongo collectd