RFR: 8083: Updates for releng projects

Fri Jun 9 23:26:08 UTC 2023

The releng projects (Local update site for building/development and Eclipse platform definition files) need some TLC.

The releng/third-party project needs some version bumps. Furthermore, for importing it as maven project into eclipse, it should have a .classpath file.

In detail, I bumped versions of the used plugins. Most significantly I updated the used jetty-maven-plugin from 9.4.46.v20220331 to 11.0.15. Seems to work out of the box, no issues. The config parameter `scanIntervalSeconds` is not recognized in that version any more.
Furthermore, I changed the maven enforcer settings to require JDK 17 and Maven 3.5.0, as in other places.

Also, the Eclipse platform URL should use https rather than http nowadays. Spolier/Outlook: To be able to use Eclipse 2023-06 I believe that we will need to find a solution to run the jetty with https. Otherwise, importing into Eclipse will not work any longer.

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Commit messages:
 - JMC-8083

Changes: https://git.openjdk.org/jmc/pull/494/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=494&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8083
  Stats: 34 lines in 5 files changed: 12 ins; 11 del; 11 mod
  Patch: https://git.openjdk.org/jmc/pull/494.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/494/head:pull/494

PR: https://git.openjdk.org/jmc/pull/494