Add a mechanism to augment marker schema for special handling purposes

From a conversation with gerald:

> For the IPC type, I don't have send/recvThreadName on my side: https://github.com/firefox-devtools/profiler/blob/main/src/profile-logic/marker-schema.js#L217-L218
> I'm guessing they're computed during processing, based on 'otherPid'. Does it mean we'll still need special front-end handling for them? Should my schema match yours and display these potential send/recvThreadName's?

I think it would be better to have these live only on the front-end. I need to add a way to merge these properties into the Gecko-provided schema.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-320)