Add support for long term archiver

[gilesknap]

We need the equivalent feature to how we specifiy which PVs go into the archiver for techUI.

@coretl maybe you can expand on this a little?

[gilesknap]

@lindap-dls has concerns about global level archiver settings and would prefer indivual IOC control - perhaps similar to what we have done for autosave. Make sure we discuss the solution with her.

[gilesknap]

Also note that we need an alarm handler solution and this has not been discussed yet.

[coretl]

Both archiver and eventually alarm handler should follow the same techui-builder style of:

• Read all the ioc.yaml files
• For each type encountered in the ioc.yaml:
  • Search for .grp in an IOC specific location
  • Fallback to search for .grp in an Beamline specific location
  • Fallback to search for .grp in a submodule
  • If .grp exists then expand it with the Entity parameters
• Push the concatenation of these expanded grp files to the archiver

The complication is how the ioc.yaml files are found. Do we just do this for main and stick it in the services repo, or do we do something fancy in the deployment repo to scan the deployed versions of things?