AssetHub Migration: Update code, tests & docs accordingly

[Imod7]

Description
With the upcoming migration of certain functionalities from the Relay Chain to Asset Hub, we need to update Sidecar by taking the following steps :

1. Update the corresponding chain-config files (assetHub*) to include the necessary endpoints for the migrated functionalities
2. Update the corresponding service files to ensure that, based on the block queried & the connected chain :
   2.1 the requested information is returned if available
   2.2 if not available, display a message redirecting the user to the correct chain
3. Add tests to reflect the above changes
4. Update already existing tests accordingly
5. Update the docs well in advance to notify the users for the upcoming changes (?)

General Notes/Actions

• Closely monitor the Asset Hub migration timeline
• Implement the above changes in the meantime
• Test once the migration is available on a test chain
• Send separate notification to bigger teams that we already support