Add silent option to backend requests

Added requests/sec(throughput)

allow to show more preview values for variables

fixed so user who can edit dashboard can edit row

Fix ineffassign issues

From review feedback:

* s/helper/metadata
* combined positional args to _request into options dict
* metadataRequest reuses _request()
* moved consumption of this.httpMethod into _request, can be overwritten
 in options due to spread-after

Signing was failing as the builds
were expected to run as ubuntu but
is run as root.

Closes #11686

Make Ldap group composed of  DNs work.

Fix for default permissions on folder are not shown as inherited in it's dashboards

added button to show more preview values for variables, button runs a function that increases options limit, fixes #11508

#9630

pkg/tsdb: fix ineffassign isues

fix CircleCI gometalinter test

graphite: use a query when testing data source

postgres: adjust timeFilter, timeFrom and timeTo macro examples

Merge branch 'annotations-created' of https://github.com/ryantxu/grafana into ryantxu-annotations-created

* When set to `true`, the `silent` option for backend_srv requests
 suppresses all event emitters that are triggered when the response is
received.
* Added `helperRequest()` to the Prometheus datasource to support
 requests that are not triggered by the user, e.g., for tab completion.
`helperRequest()` sets the `silent` option.
* Migrated all non-timeseries queries of the Prometheus datasource to
 use `helperRequest()`.

Fixes #11673