Implements an event service and demonstrates its use for sending/receiving SSL key/trust store changes

[MichaelMorrisEst]

Intended as a means to discuss what the implementation for #3074 (comment) should look like

Checklist

• Base your changes on 2.x branch if you are targeting Log4j 2; use main otherwise
• ./mvnw verify succeeds (if it fails due to code formatting issues reported by Spotless, simply run ./mvnw spotless:apply and retry)
• Non-trivial changes contain an entry file in the src/changelog/.2.x.x directory
• Tests for the changes are provided
• Commits are signed (optional, but highly recommended)

[github-actions]

Job	Requested goals	Build Tool Version	Build Outcome	Build Scan®
build-macos-latest	clean install	3.9.8	✅
build-ubuntu-latest	clean install	3.9.8	✅
build-windows-latest	clean install	3.9.8	✅

Generated by gradle/develocity-actions

[ppkarwasz]

The PR looks nice, but I need some time to analyze the existing code to see if we can reuse something. WatchManager looks reusable, but it works in a complex way.

[vy]

Instead of a fully-blown event bus that is publicly exposed, can we make this private and as small as possible, please? I agree with @ppkarwasz that we shall seek to use existing file watching mechanisms available, if possible.