fix(jcasc): remove deprecated excludeClientIPFromCrumb + silence release-drafter

[gounthar]

Summary

Two fixes backported from main to the weekly branch.

Changes

1. JCasc startup crash (dockerfiles/jenkins.yaml)

DefaultCrumbIssuer no longer accepts the excludeClientIPFromCrumb attribute in newer Jenkins/JCasc versions. The baked-in config caused a fatal UnknownAttributesException at startup, putting the controller into a restart loop.

# Before
crumbIssuer:
  standard:
    excludeClientIPFromCrumb: false

# After
crumbIssuer:
  standard: {}

Note: the plugins.txt version bumps from the main fix are not included — the weekly branch uses coverage:2.x which does not have the plugin dependency conflict.

2. Failure diagnostics step (.github/workflows/plugin_update.yml)

Adds a Capture Jenkins logs on failure step so controller logs are surfaced in CI when the workflow fails. Uses grep -m1 controller || true to avoid aborting the step under bash -e/pipefail when no container is found.

3. Release Drafter silenced (.github/workflows/release-drafter.yml)

The action fails on every push and PR event because the repo has no releases, hitting a known pagination bug in release-drafter. Triggers replaced with workflow_dispatch only.