GitLab authentication backend

If `allowed_groups` is not used with GitLab authentication, the
*read_user* scope can be used instead of *api*.

Set `BasicUserInfo.Id` in the value returned by
`SocialGitlab.UserInfo()`, in case the email address of the user changes
in GitLab. That way, the user association won't be lost in Grafana.

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