WIP: Allow dynamic fees setup for xcm-bridge

[bkontur]

The relevant change, which allows us to do dynamic pricing in pallet-xcm-bridge based on the router configuration and bridge status:

-		/// Price of single message export to the bridged consensus (`Self::BridgedNetwork`).
-		type MessageExportPrice: Get<Assets>;
+		/// Price of a single message export to the bridged consensus (`Self::BridgedNetwork`).
+		type MessageExportPrice: PriceForMessageDelivery<Id = BridgeId>;

Basically, with message bridging on AssetHub, the same dynamic price (based on the bridge congestion status) is calculated for exporting either via:

• local routing using ToRococoOverAssetHubRococoXcmRouter / ToWestendOverAssetHubWestendXcmRouter (AH<>AH transfer)
• executing ExportMessage from a sibling chain.

It is just backport of xcm-bridge/xcm-bridge-router stuff from this commit: 8ada805 (where you can see also the real usage and setup)

cc: @serban300

[serban300]

Looks good as far as I understand. But I will look more in detail while reviewing #6231

[paritytech-workflow-stopper]

All GitHub workflows were cancelled due to failure one of the required jobs.
Failed workflow url: https://github.com/paritytech/polkadot-sdk/actions/runs/16370415904
Failed job name: fmt