Upgrade Jetty from 9.4.57 to 12.1.6

[merlimat]

Motivation

This upgrades Jetty to the latest stable 12.x release, which brings improved performance, HTTP/2 and HTTP/3 support, and ongoing security updates (Jetty 9.x is EOL).

Key changes:

• Update jetty.version from 9.4.57.v20241219 to 12.1.6
• Use jetty-ee8-* artifacts to maintain javax.servlet compatibility
• Update import statements to use org.eclipse.jetty.ee8.servlet package
• Update LICENSE and NOTICE files with new artifact names and versions

Changes

(Describe: what changes you have made)

---

In order to uphold a high standard for quality for code contributions, Apache BookKeeper runs various precommit
checks for pull requests. A pull request can only be merged when it passes precommit checks.

---

Be sure to do all the following to help us incorporate your contribution
quickly and easily:

If this PR is a BookKeeper Proposal (BP):

• Make sure the PR title is formatted like:
  <BP-#>: Description of bookkeeper proposal
e.g. BP-1: 64 bits ledger is support
• Attach the master issue link in the description of this PR.
• Attach the google doc link if the BP is written in Google Doc.

Otherwise:

• Make sure the PR title is formatted like:
  <Issue #>: Description of pull request
e.g. Issue 123: Description ...
• Make sure tests pass via mvn clean apache-rat:check install spotbugs:check.
• Replace <Issue #> in the title with the actual Issue number.

---