Add AEM 6.5 LTS + Java 17 / 21 support

There is a release/650 branch, but it only compiles with Java 11, not 17 or 21 and it does not mention AEM 6.5 LTS

Could you please add support (by mentioning it in the readme's and relevant branches and updating the code)

Review the release/650 branch and the README references to AEM 6.5 LTS and Java 11. Identify the code and build constraints that prevent Java 17 or 21, then update the relevant branch and documentation. Done means the branch supports Java 17 and 21 and the README accurately describes AEM 6.5 LTS support.

Written by the indexing model from the issue text.