[improve][misc] Upgrade Jetty to 12.1.11

[lhotari]

Motivation

Keep Pulsar on the latest Jetty 12.1.x patch release. Jetty 12.1.11 release notes: https://github.com/jetty/jetty.project/releases/tag/jetty-12.1.11

Regarding security fixes: no published Jetty security advisory lists 12.1.11 as its patched version — the most recent Jetty CVEs (CVE-2026-10050 and CVE-2026-10051) were already addressed in 12.1.10, which Pulsar upgraded to previously. However, 12.1.11 contains notable robustness and availability fixes that are relevant to Pulsar's use of Jetty in the broker web service, proxy and function worker:

• Jetty 12.0.28 server becomes inaccessible with thousands of qtp threads blocked in HttpChannelState.onIdleTimeout ReentrantLock jetty/jetty.project#15226 — Server becomes inaccessible with thousands of qtp threads blocked in HttpChannelState.onIdleTimeout ReentrantLock (server lockup / availability issue)
• Massive increase in memory usage between 12.1.8 and 12.1.10 caused by ZipFileSystems jetty/jetty.project#15228 — Fix increased memory usage between 12.1.8 and 12.1.10 caused by ZipFileSystems
• Review error response codes from EagerContentHandler jetty/jetty.project#15234 — Review error response codes from EagerContentHandler

Modifications

• Bump jetty from 12.1.10 to 12.1.11 in gradle/libs.versions.toml
• Update the Jetty artifact versions in distribution/server/src/assemble/LICENSE.bin.txt and distribution/shell/src/assemble/LICENSE.bin.txt

Verifying this change

• Make sure that the change passes the CI checks.

This change is already covered by existing tests: the existing CI test coverage exercises the Jetty-based HTTP endpoints in the broker, proxy and function worker.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment