feat: enable bridged reserves from AssetHub

[dmoka]

Description

Assets bridged from other consensus systems using the new Bridge Hub system parachain are held in reserve in Asset Hub. Asset Hub contains a second instance of the pallet-assets called the foreignAssets where bridged assets are registered. Foreign assets have a parents field > 1.

Also adding reserve support for DOT coming from AssetHub.

Related Issue

Motivation and Context

Make swaps and pools using foreign assets on HydraDX, specifically assets from Snowbridge. https://github.com/Snowfork/snowbridge

How Has This Been Tested?

TODO: Add a new integration test to integration-tests/src/cross_chain_transfer.rs which tests receiving a foreign asset from assethub.

Checklist:

• [x] I have updated the documentation if necessary.
• [x] I have added tests to cover my changes, regression test if fixing an issue.
• [ ] This is a breaking change.