GitLab could already be used as an authentication backend by properly
configuring `auth.generic_oauth`, but then there was no way to authorize
users based on their GitLab group membership.

This commit adds a `auth.gitlab` backend, similar to `auth.github`, with
an `allowed_groups` option that can be set to a list of groups whose
members should be allowed access to Grafana.

Closes #12370

[skip ci]

Karma to Jest: rename and cleanup

[skip ci]

[postgres] add timescaledb option to postgres datasource

WIP Karma to Jest: heatmap renderer (refactor)

Karma to Jest: share_modal_ctrl

[skip ci]

Support timeFilter in query templating for InfluxDB

[skip ci]

Use uid when linking to dashboards internally in a dashboard

* fix: graphite function parameters should never be quoted for boolean, node, int and float types, fixes #11927

* Update gfunc.ts

* Begin conversion

* Test setup started

* Begin rewrite of graph

* Rewrite as class

* Some tests passing

* Fix binding errors

* Half tests passing

* Call buildFlotPairs. More tests passing

* All tests passing

* Remove test test

* Remove Karma test

* Make methods out of event functions

* Rename GraphElement

[skip ci]

Support client certificates for LDAP servers