Fix alert details sidebar status dropdown not closing until network request returns

The following discussion from !60960 (merged) should be addressed:

• @aturinske started a discussion: (+1 comment)

  @oregand can you review this MR? Thanks.

Implementation details

• add ref to dropdown (!61404 (merged))
• add tests

Though it's hard to test this behaviour in a Unit test without testing the Vue framework so I think what we can do is 
follow-up this merge with a feature spec (Since we really should have one anyway) and assert that the dropdown does 
in fact close on the selection of a new item regardless of if the call has resolved or not