Improve mirror queries

See merge request gitlab-org/gitlab-exporter!111

We appear to have some data integrity issues on GitLab.com where some
projects are marked as public but their namespace isn't. This project
won't actually be public and so won't get Gold features for free, so we
exclude them from the query.

Fix plan checks for mirror queries

See merge request gitlab-org/gitlab-exporter!110

Plans are no longer through namespace.plan_id, but through the root
namespace via gitlab_subscriptions.

Add Global stats

See merge request gitlab-org/gitlab-exporter!104

fix: expose runner_type directly

Closes #48

See merge request gitlab-org/gitlab-exporter!108

Before we exposed 'is_shared', but this value doesn't exist anymore since gitlab-foss@ca93faf1 so it only works previously added shared runners
I've decided to directly expose the runner_type variable, since it allows for more detailed metrics, instead of just using is_shared

Closes #48

Update pg gem to v1.2.2

See merge request gitlab-org/gitlab-exporter!107

This adds support for Ruby 2.7 and PostgreSQL 12. Omnibus is also
shipping two versions of the pg gem (v1.2.2 and v1.1.4), so let's make
this consistent.

Full list of changes:
https://github.com/ged/ruby-pg/blob/master/History.rdoc

Update redis-rb to 4.1.3 to match GitLab CE/EE

See merge request gitlab-org/gitlab-exporter!106

One bug fix: https://github.com/redis/redis-rb/blob/master/CHANGELOG.md

Update unicode-display_width (Rubocop dependency)

See merge request gitlab-org/gitlab-exporter!105

It was previously at v1.1.0, which uses the deprecated `Gem.gunzip` method.
The usage of deprecated functions was removed in unicode-display_width v1.3.3.

Add validation of metric values

Closes #60

See merge request gitlab-org/gitlab-exporter!102

Make sure to validate that when adding metric samples that the value is
a number.

Fixes: https://gitlab.com/gitlab-org/gitlab-exporter/issues/60

Limit CI builds queries to 7 days

See merge request gitlab-org/gitlab-exporter!101

This applies to EE queries only. It improves performance of those
queries significantly.

Related to https://gitlab.com/gitlab-org/gitlab-exporter/issues/58

gitlab-monitor is now called gitlab-exporter.

Rename gitlab-monitor to gitlab-exporter

See merge request gitlab-org/gitlab-monitor!100

Update Redis gem from 3.1.5 -> 4.1.2

See merge request gitlab-org/gitlab-monitor!99

This matches the change in CE and brings in support for
distributed Redis etc.