[jenkins] (BREAKING CHANGE) Enable list deprecations, drop support for old backend system, migrate away from alpha catalog service

[kurtaking]

Hey, I just made a Pull Request!

Enabled deprecation listing in bcp.json and the following deprecation cleanup is required.

• Dropped support for the old backend system, including removal of exports for JenkinsBuilder. Users must migrate to the new backend installation method.
• Replaced usage of CatalogApi from @backstage/catalog-client with CatalogService from @backstage/plugin-catalog-node
• Registered Jenkins permissions using permissionsRegistry.addPermissions(jenkinsPermissions) in the backend plugin initialization, and passed permissionsRegistry as a dependency.
• Removed redundant permission router registration from JenkinsBuilder.
• Refactored frontend app initialization to use createRoot from react-dom/client instead of react-dom, and updated how the app is created and rendered.

✔️ Checklist

• A changeset describing the change and affected packages. (more info)
• Added or updated documentation
• Tests for new functionality and regression tests for bug fixes
• Screenshots attached (for UI changes)
• All your commits have a Signed-off-by line in the message. (more info)

[backstage-goalie]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
app-next	workspaces/jenkins/packages/app-next	none	v0.0.2
@backstage-community/plugin-jenkins-backend	workspaces/jenkins/plugins/jenkins-backend	major	v0.22.0
@backstage-community/plugin-jenkins	workspaces/jenkins/plugins/jenkins	major	v0.26.0

[kurtaking]

Possibly worth doing a few of these as separate PRs, but they are required if you enable listDeprecations.