Snowbridge: Add missing runtime API

[yrong]

It looks like we missed some of the runtime API when initially merging it into fellows-runtime in PR-796, this API is required to generate proofs.

[acatangiu]

code changes look good, but CHANGELOG is messed up

We may need to apply the patch to the production branch as well as the subsequent release branches.

also, this repo doesn't use release branches since runtime artifacts are "only used once", each new release makes the previous one irrelevant/never-used-again

[bkontur]

code changes look good, but CHANGELOG is messed up

I would just revert the CHANGELOG changes (some local formatting - zepter?) and:

• either add here just one note:

## [Unreleased]

### Fixed

- [BHP](https://github.com/polkadot-fellows/runtimes/pull/978) Add missing snowbridge runtime API to the BridgeHub
  runtime.

• or add this to the Description:

- [x] Does not require a CHANGELOG entry

@yrong Are these runtimeApis relevant just for the relayer or dApps?

[yrong]

Are these runtimeApis relevant just for the relayer or dApps?

Yeah, it’s only for the relayer.

[github-actions]

Review required! Latest push from author must always be reviewed

[acatangiu]

/merge

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