GH-2092: Fuseki server

[afs]

This resolves #2902.
This resolves #2046.
This PR builds on #2894.

It adds the UI and server admin controls.

By default, the UI is served from a jar file.

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• Tests are included.
• Documentation change and updates are provided for the Apache Jena website
• Commits have been squashed to remove intermediate development commit messages.
• Key commit messages start with the issue number (GH-xxxx)

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[afs]

The check is failing because there is change in jena-fuseki-core around the internal implementation metrics which is shared with jena-fuseki-weabpp. The full build passes on GH actions (subject to previously seem effects of heavily loaded build servers - usually go away if you run the actions early European morning).

[afs]

Current state: done! the resulting combined java is the jena-fuseki-server artifact.

There are two entry points - one for the 5.2.0 "Fuseki Main" (no UI, no admin area), and one for the new full server (UI, server from the same jar file by default, admin area on disk).

The WAR file is still being built.

This completes the Java changes.

The next step is whether to switch the fuseki-server.jar in the apache-jena-fuseki. At 5.2.0, and not changed by this PR, it is the webapp+Jetty as made by maven jena-fuseki-fulljar. This is PR #2907.