feat(hive): add eels client to devnet-8 workflows

[spencer-tb]

Adds eels as a client to both devnet-8 workflows: EELS runs the
execution spec itself behind the Engine API, so consume engine
validates the fixtures directly against the spec that filled them.

• eels added to the client matrix and dispatch defaults.
• Own consume-engine flags (EELS_ENGINE_FLAGS_EELS_CLIENT): the
  shared --sim.limit includes Osaka and the BPO2→Amsterdam
  transition, which the eels client refuses by design (Amsterdam from
  genesis only), so its rows run .*fork_Amsterdam-.* (quick:
  combined with the EIP filter).
• Excluded from consume-rlp (no /chain.rlp import) and
  execute-blobs (no transaction submission).
• No client_repos/client_images entries: the client builds from
  its Dockerfile defaults in hive, so common_client_tag does not
  apply to it.

Verified locally against glamsterdam-devnet@v8.1.0 (consume-engine,
.*fork_Amsterdam-.*): 0 failures so far in an in-progress 24,819-test
sweep; a 136-test subset passed 136/136.

Draft until the client lands in hive (ethereum/hive#1596, which itself
follows ethereum/execution-specs#3363).