Bumped mysql2 gem version from 0.4.5 to 0.4.10.

See merge request gitlab-org/gitlab-ce!16034

Incorporate Gitaly's RemoteService RPCs

Closes gitaly#852

See merge request gitlab-org/gitlab-ce!16060

Signed-off-by: Rémy Coutable <remy@rymai.me>

Uses `list_commits_by_oid` on the CommitService, to request the needed
commits for pipelines. These commits are needed to display the user that
created the commit and the commit title.

This includes fixes for tests failing that depended on the commit
being `nil`. However, now these are batch loaded, this doesn't happen
anymore and the commits are an instance of BatchLoader.

Replace factory_girl_rails with factory_bot_rails

See merge request gitlab-org/gitlab-ce!15919

Migrate Gitlab::Git::Repository#merge_base_commit to Gitaly

Closes gitaly#808

See merge request gitlab-org/gitlab-ce!15770

I've followed the [upgrade guide](https://github.com/thoughtbot/factory_bot/blob/4-9-0-stable/UPGRADE_FROM_FACTORY_GIRL.md) and ran these two commands:

```
grep -e FactoryGirl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|FactoryGirl|FactoryBot|"
grep -e factory_girl **/*.rake **/*.rb -s -l | xargs sed -i "" "s|factory_girl|factory_bot|"
```

Signed-off-by: Rémy Coutable <remy@rymai.me>

- Added an ActiveSupport (using Rails.cache) caching adapter
- Overview of the new features can be found at https://johnnunemaker.com/flippin-features-at-runtime/
- Full Changelog can be found at https://github.com/jnunemaker/flipper/blob/v0.11.0/Changelog.md

Signed-off-by: Rémy Coutable <remy@rymai.me>