Enable the EmptyRule SCSS Linter

Prevents empty SCSS rules from being included in the SCSS.

Also fixes the handful of lints caught by the linter.

Regarding the `.gh` rule in monokai.scss, which was added in [this commit](https://gitlab.com/gitlab-org/gitlab-ce/commit/bf079c24afb8ad2991a4eaf60a71a7bc45dd775d), it appears to be empty in [the original file as well](https://github.com/richleland/pygments-css/blob/master/monokai.css). So I think it's fine to delete the selector.

cc: @jschatz1 

See merge request !3769

Updated list of InfluxDB queries/config

See merge request !3840

This setup is quite a bit different from before. In the previous setup
raw data was kept around for 30 days and downsampled data for 7 days.
This became problematic for GitLab.com as the number of points and
series resulted in InfluxDB running out of memory when starting up
(besides taking up 30 GB of storage).

To work around this the new setup keeps raw data around for _only_ an
hour while keeping downsampled data around for 7 days. In turn all
Grafana dashboards _only_ query the downsampled data instead of also
querying raw data.

Based on rough calculations this setup needs around 2GB of storage for 1
week of data, excluding whatever is needed for storing the raw data
(this highly depends on the amount of traffic).

If users want to use this new setup they have to remove any existing
dashboards provided by GitLab.com and re-import the ones from the
Grafana dashboards repository
(https://gitlab.com/gitlab-org/grafana-dashboards/). Should users wish
to change their default retention policy the easiest way of doing so is
to simply drop the database and re-run the InfluxDB commands added by
this commit. Users who want to keep their default retention policy as-is
can simply create the "downsampled" policy and run the other commands.

[ci skip]
Signed-off-by: Rémy Coutable <remy@rymai.me>

Fix license detection to detect all license files, not only known licenses

Fixes #15470.

See merge request !3878

Prevent users from deleting Webhooks via API they do not own

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15576

See merge request !1959

Fixes #15470.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Add posibility to define a hidden job without 'script' in .gitlab-ci.yml

References #15451

/cc @ayufan 

See merge request !3849

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15576

Hiding future dates on contribution calendar

Fixes #9036

See merge request !2628

Allow middle-click on a Todo row to open in a new tab



See merge request !3899

Add --tags to fetching gitlab-shell to ensure tags are downloaded

Closes #15525

See merge request !3896

Closes #15525

Update Sidekiq and related gems (bundle update sidekiq)

Closes #15079

See merge request !3817

Re-generate Spring binstubs for updated version of Spring

Prevents output like this:

    Array values in the parameter are deprecated. Please use a String or nil.
    An Array was passed in from bin/rspec:3:in `load'

See merge request !3887

[ci skip]

Prevents output like this:

    Array values in the parameter are deprecated. Please use a String or nil.
    An Array was passed in from bin/rspec:3:in `load'

Fix broken link in HA docs

Whoops! Fix broken link in docs from gitlab-org/gitlab-ce!3579

See merge request !3890

Updated HA docs and open to public

Closes https://dev.gitlab.org/gitlab/organization/issues/624

We still need to go through the old gitlab.com/standard/high-availability and move relevant docs over, plus do some docs on DRBD. However, I think this is a good volume for the first pass. Can we get this out there and then iterate?

cc/ @axil @patricio For your review, please.

See merge request !3579

Add Sidekiq troubleshooting docs

Closes #15287 

cc/ @stanhu @jacobvosmaer @dstanley

See merge request !3802

Refactor Todos feature spec to be faster and less brittle

We now only create two Todos instead of 21 when testing pagination, and
we've updated the test to be less brittle when dealing with slower CI
environments.

See merge request !3889

Use the `can?` helper instead of `current_user.can?`

Fixes #15513.

See merge request !3882

We now only create two Todos instead of 21 when testing pagination, and
we've updated the test to be less brittle when dealing with slower CI
environments.

Correctly escapes label title in filters

Fixes #15522

See merge request !3880

Move cherry-pick feature specs to proper directory

Cherry pick feature specs were located in `spec/feature/project` directory while we have `spec/feature/projects`.

Later location is consistent with our namespaces (we have `Projects::` namespace, not `Project::`).

See merge request !3875

Bump gitlab-shell to 2.7.2

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15525

See merge request !3884

[ci skip]

Add tests for filtering owned projects

REF: #3799

See merge request !3873