XCM FeeManager & PriceForSibling/ParentDelivery integration

[Dinonard]

Once the approach with PriceForSiblingDelivery and PriceForParentDelivery is more widely adopted, in respect to XCM fee estimation, integrate it into our runtimes.

A solution for better XCM price estimation should be available in the first half of 2024.

Related issues to usability:

• Estimate Fees for XCM paritytech/polkadot-sdk#690
• Better delivery fees: PayFees paritytech/polkadot-sdk#3434

[ipapandinas]

August update:

In uplift v1.11 we added XcmPaymentApi that provides an API to estimate XCM fees. On next uplift to v1.13, we should add DryRunApi to complete the implementation for dry run information on extrinsics and remote XCM. Example of runtimes integrating this: paritytech/polkadot-sdk#4634

Next V5 version brings a new mechanism to pay for fees: PayFees, that takes into account delivery fees in addition to remote execution fees. Related issue: paritytech/polkadot-sdk#5420

[Dinonard]

To follow up on this, BuyExecution still hasn't been deprecated as the RFC states it would be.

Probably the best course of action for now is to let this be and wait until PayFees becomes exclusive (or at least mainstream).