This PR includes the following 2 improvements:

## Ethereum Client

Author: @yrong 
### Original Upstream PRs
- https://github.com/Snowfork/polkadot-sdk/pull/123
- https://github.com/Snowfork/polkadot-sdk/pull/125

### Description
The Ethereum client syncs beacon headers as they are finalized, and
imports every execution header. When a message is received, it is
verified against the import execution header. This is unnecessary, since
the execution header can be sent with the message as proof. The recent
Deneb Ethereum upgrade made it easier to locate the relevant beacon
header from an execution header, and so this improvement was made
possible. This resolves a concern @svyatonik had in our initial Rococo
PR:
https://github.com/paritytech/polkadot-sdk/pull/2522#discussion_r1431270691

## Inbound Queue

Author: @yrong 
### Original Upstream PR
- https://github.com/Snowfork/polkadot-sdk/pull/118

### Description
When the AH sovereign account (who pays relayer rewards) is depleted,
the inbound message will not fail. The relayer just will not receive
rewards.

Both these changes were done by @yrong, many thanks. ❤

️

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Co-authored-by: claravanstaden <Cats 4 life!>
Co-authored-by: Ron <[email protected]>
Co-authored-by: Vincent Geddes <[email protected]>
Co-authored-by: Svyatoslav Nikolsky <[email protected]>