Archive appliance: get IOCs to tell archive appliance about archivable PVs on start

# Issue Description

As a developer I would like each IOC to notify the archive appliance about the PVs that the inst archiver should archive, as that IOC starts.

### How & Where?

- The archive appliance has REST APIs to add PVs to archive
- We already have curl as a support module that is capable of sending http requests
- At ioc startup time, use `curl` (or equivalent) to send a HTTP request to the archiver to cause it to archive any PVs marked with `info(archive, ...)`.

### Additional Information

We already have a `postIocInit.cmd` (in `C:\Instrument\Apps\EPICS\iocstartup`) that may be a suitable place to trigger this from all IOCs.

As the archive will be central, we can notify a fixed URL, but that URL should be defined in a single central place not in each IOC individually.

# Acceptance Criteria

- [ ] As an IOC starts, it causes the new central inst archiver to archive any relevant PVs.

# How to Review
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