Previously `Step` parameter would set a hard value for any zoom level.

Now it's renamed to `Min step` and sets the minimal value of `step` parameter
to Prometheus query. User would usually want to set it to the scraping interval
of the target metric to avoid having shap cliffs on graphs and extra load
on Prometheus. Actual `step` value is calculated as the minimum of automatically
selected step (based on zoom level) and user provided minimal step. If user
did not provide the step, then automatic value is used as is.

Example bahavior for `60s` scrape intervals:

* `5s` automatic interval, no user specified min step:
  * Before: `step=5`
  * After: `step=5`
* `5s` automatic interval, `1m` user specified min step:
  * Before: `step=5`
  * After: `step=60`
* `5m` automatic interval, `1m` user specified min step:
  * Before: `step=60` (not really visible, too dense)
  * After: `step=300` (automatic value is picked)

See:

* https://github.com/grafana/grafana/issues/8065
* https://github.com/prometheus/prometheus/issues/2564

bind create annotation handler directly to plotclick event, not to global graph-click

pass ctrlKey and metaKey through flot events

Tab size was added as 2 in .editorconfig but a tab size of 4 is used
throughout go code base.

This can cause editors such as vscode to automatically reformat open .go
files to tab size 2 from 4.

plugins: refactoring builtIn data source concept, now means data source plugins that you do not need to add via data sources page, that is automatically added as selectable data source, #8095

Merge branch 'always_displayed_datasources' of https://github.com/ctide/grafana into ctide-always_displayed_datasources