Allow Grafana Assume Role (`awsDatasouresTempCredentials`) for Redshift

[skeilson]

Is your feature request related to a problem? Please describe.
Currently the Grafana Assume Role authentication feature toggle permits AWS authenticaton via simpler, more streamlined means. At this time, this feature is currently limited to Cloudwatch, only.

It would be great to open this up for other AWS resources, in particular, Redshift data sources

Describe the solution you'd like
Permit the Grafana Assume Role feature for Redshift data sources

Describe alternatives you've considered
n/a as there are other auth options. This would be a great feature to add.

Additional context
n/a

[chrijun]

This would a very useful feature for us!

[kundkingan]

Same, we need it!