SQL Datasources: Move database setting to jsonData (#58649)

* Datasource settings: Add deprecation notice for database field

* SQL Datasources: Migrate from settings.database to settings.jsonData.database

* Check jsonData first

* Remove comment from docs

docs/sources/datasources/postgres/_index.md

@@ -125,11 +125,11 @@ datasources:
   - name: Postgres
     type: postgres
     url: localhost:5432
-    database: grafana
     user: grafana
     secureJsonData:
       password: 'Password!'
     jsonData:
+      database: grafana
       sslmode: 'disable' # disable/require/verify-ca/verify-full
       maxOpenConns: 0 # Grafana v5.4+
       maxIdleConns: 2 # Grafana v5.4+