Merge branch 'deployment-tracking' into 'master'

Added Rake task for tracking deployments

## What does this MR do?

This MR adds a Rake task to track the current version of GitLab in InfluxDB.

## Are there points in the code the reviewer needs to double check?

We may want to document this Rake task in some Markdown file, but I'm not sure what the best place for this would be.

## Why was this MR needed?

We want to have a more accurate overview of when deployments occurred. 

## What are the relevant issue numbers?

https://gitlab.com/gitlab-com/infrastructure/issues/98

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] ~~API support added~~
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5320

CHANGELOG

@@ -34,6 +34,7 @@ v 8.10.0 (unreleased)
   - Support U2F devices in Firefox. !5177
   - Fix issue, preventing users w/o push access to sort tags !5105 (redetection)
   - Add Spring EmojiOne updates.
+  - Added Rake task for tracking deployments !5320
   - Fix fetching LFS objects for private CI projects
   - Add the new 2016 Emoji! Adds 72 new emoji including bacon, facepalm, and selfie. !5237
   - Add syntax for multiline blockquote using `>>>` fence !3954

doc/raketasks/maintenance.md

@@ -167,3 +167,22 @@ of those assets. Unless you are modifying the JavaScript / CSS code on your
 production machine after installing the package, there should be no reason to redo
 rake assets:precompile on the production machine. If you suspect that assets
 have been corrupted, you should reinstall the omnibus package.
+
+## Tracking Deployments
+
+GitLab provides a Rake task that lets you track deployments in GitLab
+Performance Monitoring. This Rake task simply stores the current GitLab version
+in the GitLab Performance Monitoring database.
+
+For Omnibus-packages:
+
+```
+sudo gitlab-rake gitlab:track_deployment
+```
+
+For installations from source:
+
+```
+cd /home/git/gitlab
+sudo -u git -H bundle exec rake gitlab:track_deployment RAILS_ENV=production
+```

lib/tasks/gitlab/track_deployment.rake

+namespace :gitlab do
+  desc 'GitLab | Tracks a deployment in GitLab Performance Monitoring'
+  task track_deployment: :environment do
+    metric = Gitlab::Metrics::Metric.
+      new('deployments', version: Gitlab::VERSION)
+
+    Gitlab::Metrics.submit_metrics([metric.to_hash])
+  end
+end