Remove base_url, add external_url & internal_url

[frenck]

Proposed change

This PR updates the documentation for the parent PR.

Removes the use of base_url from our documentation, as it is deprecated.
Insert external_url and internal_url core configuration as the replacements.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logo's and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: Add get_url helper, deprecate base_url core#35224
• Link to frontend pull request: Add new core configuration UI for external_url & internal_url frontend#5755
• Link to JavaScript WebSocket pull request: Add new external & internal URL core configs to HassConfig home-assistant-js-websocket#115
• Link to parent pull request in the Brands repository:
• This PR fixes or closes issue:

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

[frenck]

Done!