[FEATURE] Sequencer admin contract to encapsulate keys (and namespace) within execution client state root

## Is your feature request related to a problem? Please describe.

Yes, we would like to encapsulate the public key of the sequencer within the state root of the execution client to avoid having to validate it independently for proving state transition and data availability.

Furthermore, this design lends itself to support key rotation for the sequencer software. Which is an issue independent of this, but it would be great to kill two birds with one stone.

## Describe the solution you'd like

Spoke with @tac0turtle about requesting the state root to include the sequencer's public key as well as the namespace it posts data to.

He mentioned that it could be possible to use existing staking contracts.

## Describe alternatives you've considered

Currently we verify the namespace and public key of the sequencer independently of the execution client state root. But ideally we can reduce it to only the state root if those fields are encapsulated within it.

## Additional context

n/a

No files, tests, or entry points are identified in the issue. Start by reviewing how the execution client state root currently relates to the sequencer namespace and public key, then examine whether existing staking contracts could represent those fields; done means an agreed implementation that lets the state root provide both values and supports the proposed validation change.

Written by the indexing model from the issue text.