URL drilldown docs

[streamich]

• Add user facing docs for URL drilldown.

Part of #55324

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[Dosant]

docs draft: https://docs.google.com/document/d/1LQ-Viu8aaav4CUAuiVGV1sPKdP-4AoXXgRlP9Nw5WiA/edit#
URL drilldown pr: #75450

In addition to adding new URL drilldown page, we should also update existing drilldown docs:
https://www.elastic.co/guide/en/kibana/current/drilldowns.html

This page assumes that "Go to dashboard" is the only drilldown type available, but it isn't true with new URL drilldown

probably docs structure should go like this:

• Dashboard
  • Drilldowns
    • Overview
    • Go to Dashboard
    • Go to URL

cc @elastic-jb @mdefazio @streamich

[elasticmachine]

Pinging @elastic/kibana-docs (Team:Docs)

[gchaps]

@Dosant I can with a review of your doc.