support template variable in stat field

docs: improve ES provisioning examples

Fix megacheck issues

closes #12281

[skip ci]

fix panel solo size

Fix doc error for DingDIng alert

Update the regex-matching in templateSrv to work with the new variabl…

Fix cannot receive dingding alert when alert message is empty

[skip ci]

[skip ci]

[skip ci]

Delete provisioning meta data when deleting Folder

prior to this fix Grafana didnt delete meta data
about the provisioned dashboard in `dashboard_provisioning`
which means that the dashboard wasn't inserted into
Grafana again if the folder was delete within Grafana.

closes #13280

Update the regex-matching in templateSrv to work with the new variable-syntax and be more flexible to regex-changes #13804

Explore: fix graph resize on window resize

[skip ci]

[skip ci]

Fix click-based selection of typeahead suggestion

- resize HOC wrapper only resized first child which in case of large
  graphs was the warning button
- moved warning button inside the panel parent

Explore: query transactions for faster result display

* stackdriver: add resource type to filter and group bys

* stackdriver: remove not used param

* stackdriver: refactor filter and group by code

* stackdriver: remove resource type if its already in filter list

* stackdriver: remove debug logging

* stackdriver: remove more debug logging

* stackdriver: append resource type to legend name if there are more than one type present in the response

* stackdriver: only make new request if filter has real value

* stackdriver: format legend support for resource type

* stackdriver: add resource type to documentation

* stackdriver: not returning promise from query function

* stackdriver: fix refactoring bug

* stackdriver: remove not used import

[skip ci]