This adds an option to the postgres datasource config for
timescaledb support. When set to auto it will check for
timescaledb when testing the datasource.

When this option is enabled the $__timeGroup macro will
use the time_bucket function from timescaledb to group
times by an interval.

This also passes the datasource edit control to testDatasource
to allow for setting additional settings, this might be useful
for other datasources aswell which have optional or version
dependant features which can be queried.

This Dockerfile allows anyone with a recent version of Docker to quickly build a fully working Grafana container without any local build tooling. Pulling the sources from Git and calling `docker build .` is enough.

* Explore: Query hints for prometheus

- time series are analyzed on response
- hints are shown per query
- some hints have fixes
- fix rendered as link after hint
- click on fix executes the fix action

* Added tests for determineQueryHints()

* Fix index for rate hints in explore

[skip ci]

Add fill mode to fill in previously seen value when point is missing to SQL datasources

Fixing bug in url query reader and added test cases

[skip ci]

Fix issue with secret fields after updating datasource

fix missing *

The missing * causes the text to be in the box to be displayed incorrectly.

Explore: prometheus query helpers 

- use color variables for cascader styles
- fix Table value type

[skip ci]

WIP: Fit panels to screen height

- load all histogrammable metrics on start, based on `{le!=''}` series
  query
- select dropdown shows all those metrics as well as histograms in a
  special group
- select a metric will write fill the metric in the query box
- if a histogram is chosen, it will write a complete
  `histogram_quantile` query
- added new dependency: rc-cascader

- clears the content of a query row

- Clear All button to clear all queries and results
- moved result viewer buttons below query rows to make it more clear
  that they govern result options

Explore: show message if queries did not return data

- every result viewer displays a message that it received an empty data
  set

- position was determined by SPACE, but Prometheus selectors can
  contain spaces
- added negative lookahead to check if space is outside a selector
- moved braces plugin into PromQueryField since braces are prom specific