Move STS field definitions into actorkeys dictionary

The fixed STS radio IDs are enumerated in the alertsActor STS.yaml file. That does not have all the fields which STS needs, and will become unwieldy with more cryostats: we want to change the way this is done.

The main idea is to assign 100 STS IDs to each cryostat and SM, and to put those in a new stsOffset actorkeys dictionary field. Then from that generate STS.yaml for all the cryostats, where the individual items contain all the fields the alertsActor and the STS needs: (mhsKeywordName, mhsKeywordIdx, stsRadioID, stsDatatype, stsDescription).

Two sub tickets: for adding the stsOffset actorKeys slot, and for reading actorKeys and generating the STS.yaml file.