Allow extra_apex_payload_key to take multiple names at once

When running tests, we might need to add many
extra_payload_keys. Currently we have to add --extra_apex_payload_key
for each key pair we pass, resulting in extremely long argument list.

Test: th
Bug: 239991438
Change-Id: I3e5f9d76c7f45822fb986b603dc089407c35b76b