* The main driver for this change was to make the read from a.newFragmentCh timeout quickly rather than waiting for the test timeout (much longer). While testing the change I observed a panic during shutdown, but it was swallowed and moreover there was no stack trace so it wasn't obvious. I'm hoping we can get rid of the recover, so I fixed the issue in the activitylog tests that needed it.
* sketch out partial month activity log client API
* unit test partialMonthClientCount
* cleanup api
* add api doc, fix test, update api nomenclature to match existing
* cleanup
* add PR changelog file
* integration test for API
* report entities and tokens separately
* fix racy activity log tests and move testing utilities elsewhere
* remove TODO
* move SetEnable out of activity log
* clarify not waiting on waitgroup
* remove todo
* merge activity log invalidation work from vault-enterprise PR 1546
* skip failing test due to enabled config on oss
Co-authored-by: Mark Gritter <mgritter@hashicorp.com>