Investigate event mapper replacement

[cmgrote]

Investigate the potential to replace the current (likely-not-very-scalable) event mapper implementation for this proxy with one that is more scalable -- probably based on the v11.7 events topic that includes more details about the specific changes that were made. In an ideal scenario, this would allow us to avoid any need to persist state separately: is that feasible?

If so, we could then re-implement the event mapper without any reliance on stubs, but with a minimum v11.7 requirement for Information Server. For v11.5 we could still provide a read-only proxy connector, just without any (optional) event mapper connector for that earlier release.

[cmgrote]

The IgcUnifiedGovEvents topic is not a solution on its own, as it does not have any published events from IMAM activity (that only appears to go to the InfosphereEvents topic); however, the InfosphereEvents topic has published IMAM activity in it whether events are enabled or not in IGC.

There may therefore be a potential solution by combining only the IMAM-related events from InfosphereEvents and the full set of events from IgcUnifiedGovEvents (?)

[cmgrote]

Caveats identified in using IgcUnifiedGovEvents:

• does not appear to include events for various imported things (eg. imported relationships)
• uses a different set of identifiers for changes (eg. ASSET_FIELD and RELATION indicating the field that has changed does not match the REST property name, but instead values like assignedAssetsExcludingTerms_clean and assignedToTerms_clean -- which are not resolvable from the type system accessible via API)