feat(node/rpc): `admin_sequencerActive` RPC Method Support

### Description

Add support for the [`admin_sequencerActive`](https://github.com/ethereum-optimism/optimism/blob/develop/op-node/node/api.go#L73-L75) RPC endpoint in the `kona-node`.

Additional context: [Sequencer RPC endpoints](https://github.com/ethereum-optimism/optimism/blob/develop/op-node/node/api.go#L65-L75).