update/alert.v1: Add SenderStatus model

SenderStatus is set to be replacing endpoint errors in the near future.

Additionally it seems that MsGraphSendMail changes have not made it
to cloudvision-apis repo but are merged in arista repos vendor.
Updating alert.proto to reflect those changes.

[GENERATED_COMMIT]

Change-Id: Ibfe1383d0888d3021814c8326f10bd05c4f72bf6

Author: Arista-Jenkins