Wait for all sub routines to finish before closing Grafana

The datasource uses the default region in the query if the region
is "" in the settings. However setting the region to an empty string
is almost impossible and rendered incorrectly.

This commit introduces a special value "default" for region which
is shown in the drop down and is translated to the default region
of the data source when performing queries.

simple solution for waiting for all go sub routines to
finish before closing Grafana. We would use errGroup
here as well but I dont like spreading context's all
over the place.

closes #10131

Solves problem with Github authentication restriction by organization

* change $__timeGroup macro to include column alias

* update docs and help text for $__timeGroup macro

Load dashboards from disk into the database at regular interval

* mysql: pass timerange for template variable queries

* mysql: document time range macro usage in template variables

* mysql: docs for on time range change refresh mode for template queries

* Revert "mysql: docs for on time range change refresh mode for template queries"

This reverts commit 5325972aa4f66257aa20f7ae6d4de8fa8fe628b6.

Solves problem with Github authentication restriction by organization membership when the organization's access policy is set to "Access restricted". "Access restricted" policy should not stop user to authenticate.

How it is solved:
* Take organizations_url field data from user basic data response
* Make another request to get all organization the user is a member of (public membership)
* Authenticate user if appropriate organization found in that list

* pass timerange for template queries when refresh is set to timerange
change

* document on time range change refresh mode for template queries

named metric is present