Show leader nodes in Services Tab

[FrankChen021]

This PR is a replacement for #10418 .

The core changes at the server side in #10418 has been implemented in #10680, and based on that implementation, a is_leader column is added to 'servers' table which means user could know which nodes are playing in a role of leader by querying 'servers' table.

This PR provides a more convenient, intuitive way for users to get leader information - by showing the information in 'Details' column under 'Services' tab.

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[FrankChen021]

Hi @vogievetsky , Could you help review this PR ?

[clintropolis]

lgtm 👍

[vogievetsky]

Looks great. Very helpful