[skip-ci] [data.search.session] Add extend functionality and expose route

[lukasolson]

Summary

Requires #86815.

Adds a new method on the enhanced search session service to extend the TTL on a search session, which includes updating the expires timestamp in the saved object as well as extending each individual search request's keep_alive.

Exposes this method through a route, and adds a utility method to the client-side session client.

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[lukasolson]

Superseded by #87966.