Show a 'Success' banner on Manage Jenkins page save

[janfaracik]

In the new Manage Jenkins world, it doesn't make sense to redirect users after saving a page (and it could be argued it never did). This PR fixes that, keeping users on the same page when they hit save and displays a nice little notification to indicate that the save was successful. Based on PR comments, also removed the 'Apply' button for experimental pages as with this new experience it doesn't make sense.

Precursor to making the new Manage Jenkins UX the default.

Testing done

• Clicking Save on a Manage Jenkins page stays on the page
• A 'Success' banner appears

Screenshots (UI changes only)

Proposed changelog entries

• Show a 'Success' banner on Manage Jenkins page save

Proposed changelog category

/label web-ui,rfe

Proposed upgrade guidelines

N/A

Submitter checklist

• The issue, if it exists, is well-described.
• The changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developers, depending on the change) and are in the imperative mood (see examples). Fill in the Proposed upgrade guidelines section only if there are breaking changes or changes that may require extra steps from users during upgrade.
• There is automated testing or an explanation as to why this change has no tests.
• New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadocs, as appropriate.
• New deprecations are annotated with @Deprecated(since = "TODO") or @Deprecated(forRemoval = true, since = "TODO"), if applicable.
• UI changes do not introduce regressions when enforcing the current default rules of Content Security Policy Plugin. In particular, new or substantially changed JavaScript is not defined inline and does not call eval to ease future introduction of Content Security Policy (CSP) directives (see documentation).
• For dependency updates, there are links to external changelogs and, if possible, full differentials.
• For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers

@mention

Before the changes are marked as ready-for-merge:

Maintainer checklist

• There are at least two (2) approvals for the pull request and no outstanding requests for change.
• Conversations in the pull request are over, or it is explicit that a reviewer is not blocking the change.
• Changelog entries in the pull request title and/or Proposed changelog entries are accurate, human-readable, and in the imperative mood.
• Proper changelog labels are set so that the changelog can be generated automatically.
• If the change needs additional upgrade steps from users, the upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the pull request title (see example).
• If it would make sense to backport the change to LTS, be a Bug or Improvement, and either the issue or pull request must be labeled as lts-candidate to be considered.

[mawinter69]

Now the save button does the same as the apply button? Then we can remove one of them

[janfaracik]

Now the save button does the same as the apply button? Then we can remove one of them

I agree. Thoughts on me doing it is as part of this PR or a follow up?

[timja]

Now the save button does the same as the apply button? Then we can remove one of them

I agree. Thoughts on me doing it is as part of this PR or a follow up?

makes sense to do this but only in the new version

[timja]

LGTM

[timja]

Could you update the screenshot in the description?

[janfaracik]

Now the save button does the same as the apply button? Then we can remove one of them

Happy with this @mawinter69 ?