Add versioning and support policy information

[ppkarwasz]

This PR adds information about the support status of various Apache Log4j releases.

Related to #1867

[ppkarwasz]

Closes #3988

@vy, sorry for the force push, but this PR has been opened for so long that I totally forgot it was already submitted.

[FreeAndNil]

LGTM

[vy]

I haven't reviewed the most recent changes yet. But in its current state, it creates yet another page that needs to be updated during a release, and we should not merge this without reflecting this on the release instructions.

Can we programmatically populate this content? Reuse some existing properties in pom.xml? (Adding yet another property to pom.xml that needs to be manually updated during a release is not a better option.)

[ppkarwasz]

I added more precise release instructions in apache/logging-parent#453, but lifecycle documentation can’t really be automated today. Lifecycle events (endOfDevelopment, endOfSupport, endOfLife) depend on PMC policy decisions and must be applied manually by the release manager.

ATR will simplify this in the future (see apache/tooling-trusted-releases#183), so adding project-specific automation now doesn’t seem worthwhile.

The Log4j release automation you built has saved days of work across a dozen releases and is finally paying off. Automating lifecycle information would offer far smaller benefits.

[vy]

I've tried to shorten the content (e.g., no need to list versions in the policy page) and fixed/improved some typesetting. I still think this is a maintenance burden for a feature that no user has asked for. If it happens to be forgotten during a release, I trust that @FreeAndNil and @ppkarwasz will volunteer to fix it.