* TemplateSrv: deprecates templateSrv.variables and adds getVariables

* Update public/app/plugins/datasource/postgres/query_ctrl.ts

Co-Authored-By: Dominik Prokop <dominik.prokop@grafana.com>

* Update public/app/plugins/datasource/stackdriver/components/VariableQueryEditor.test.tsx

Co-Authored-By: Dominik Prokop <dominik.prokop@grafana.com>

* Update public/app/plugins/datasource/cloudwatch/datasource.ts

Co-Authored-By: Dominik Prokop <dominik.prokop@grafana.com>

* Update public/app/plugins/datasource/mysql/query_ctrl.ts

Co-Authored-By: Dominik Prokop <dominik.prokop@grafana.com>

* Chore: updates after PR comments

Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>