[Feature request] Provide support for Oracle as backend database for grafana.

### Discussed in https://github.com/grafana/grafana/discussions/51481 <div type='discussions-op-text'> ^{Originally posted by **niranjanpai** June 13, 2017} Grafana currently supports mysql, sqllite and postgres as backend databases. Can we add support for Oracle also as a backend database? We should be able to store user details, dashboards and sessions in Oracle. - What Grafana version are you using? 4.2</div>