* Remove URL-based alertmanagers from endpoint config
* WIP
* Add migration and alertmanagers from admin_configuration
* Empty comment removed
* set BasicAuth true when user is present in url
* Remove Alertmanagers from GET /admin_config payload
* Remove URL-based alertmanager configuration from UI
* Fix new uid generation in external alertmanagers migration
* Fix tests for URL-based external alertmanagers
* Fix API tests
* Add more tests, move migration code to separate file, and remove possible am duplicate urls
* Fix edge cases in migration
* Fix imports
* Remove useless fields and fix created_at/updated_at retrieval
Co-authored-by: George Robinson <george.robinson@grafana.com>
Co-authored-by: Konrad Lalik <konrad.lalik@grafana.com>
