* (WIP) send alerts to external, internal, or both alertmanagers
* Modify admin configuration endpoint, update swagger docs
* Integration test for admin config updated
* Code review changes
* Fix alertmanagers choice not changing bug, add unit test
* Add AlertmanagersChoice as enum in swagger, code review changes
* Fix API and tests errors
* Change enum from int to string, use 'SendAlertsTo' instead of 'AlertmanagerChoice' where necessary
* Fix tests to reflect last changes
* Keep senders running when alerts are handled just internally
* Check if any external AM has been discovered before sending alerts, update tests
* remove duplicate data from logs
* update comment
* represent alertmanagers choice as an int instead of a string
* default alertmanagers choice to all alertmanagers, test cases
* update definitions and generate spec