initial integration of mission dispatch, coordinated from platform agent

PR similar to https://github.com/ooici/coi-services/pull/2040, which somehow got messed up with duplicate commits. I manually "squashed" them in this new PR. 

@edwardhunter review/merge.
@Bobfrat review

- latest changes in Bob's mission executive.
- new integration tests to exercise mission execution via platform agent, one in COMMAND state and the other in MONITORING (aka, streaming) state.
- removed some initial placeholders for the tests

Related tests are completing OK locally, but have been skipped for this PR to not "interfere" (in terms of extra delays) with buildbots just yet.  (BTW, do we need an especial buildbot for platform related tests?)