Enable public dashboards with athena datasource

[maczikasz]

Is your feature request related to a problem? Please describe.
Support the Publid dashboards feature of grafana, athena is listed as "unconfirmed" here https://grafana.com/docs/grafana/latest/dashboards/dashboard-public/

Describe the solution you'd like
I have a set of dashboards that I want to publish using the public dashboards feature, but as they depend on the data source, and the athena does not support that currently

Describe alternatives you've considered
There is no proper alternative, only either making them anonymus read or giving out user credentials

[katebrenner]

may be fixed by #312