Security: Store datasource passwords encrypted in secureJsonData (#16175)

* Store passwords in secureJsonData

* Revert unnecessary refactors

* Fix for nil jsonSecureData value

* Remove copied encryption code from migration

* Fix wrong field reference

* Remove migration and provisioning changes

* Use password getters in datasource proxy

* Refactor password handling in datasource configs

* Add provisioning warnings

* Update documentation

* Remove migration command, moved to separate PR

* Remove unused code

* Set the upgrade version

* Remove unused code

* Remove double reference

pkg/tsdb/prometheus/prometheus.go

@@ -70,7 +70,7 @@ func (e *PrometheusExecutor) getClient(dsInfo *models.DataSource) (apiv1.API, er
 		cfg.RoundTripper = basicAuthTransport{
 			Transport: e.Transport,
 			username:  dsInfo.BasicAuthUser,
-			password:  dsInfo.BasicAuthPassword,
+			password:  dsInfo.DecryptedBasicAuthPassword(),
 		}
 	}