mssql: pass timerange for template variable queries

[cgaborik]

atm the frontend does not pass the timerange on template variable queries in mssql. this patch changes the behaviour to include the timerange when the refresh mode for the variable is set to on time range change

I've updated the mssql datasource.ts file and tested, but I'm still navigating how to publish this change.

[marefr]

To fix this you can have a look at the MySQL datasource code which already has solved this. The needed code is highlighted.

Basically we need the same code as highlighted for MySQL above implemented in the MSSQL datasource code.

As a bonus, to validate that your implemented changes are correct a test could be added here and would be similar to one of the existing tests. However, instead of verifying the response is correct you would need to verify that the payload provided to this.backendSrv.datasourceRequest includes a data property with to and from properties having a value according to argument passed to metricFindQuery.

[cgaborik]

I've had it working for some time on our local Grafana instance. I think I merged the datasource.ts file correctly with cgaborik@0ed8fb3

[marefr]

@cgaborik with that merge you've basically merged your PR to your fork of Grafana. Should be pretty straight forward to extract that commit onto new branch based on latest Grafana master and open PR here. If you're interested of course we would love the contribution.