Grpc stateless gloas

[james-prysm]

What type of PR is this?
Feature

What does this PR do? Why is it needed?

introduces the -- stateless flag for grpc and updates grpc to match rest in terms of blinded envelope use for stateful path which is the default.

test configs

# Controlled counterfactual (inverse of gloas-config-nostateless.yml): identical config but with
# --stateless on EVERY validator. If slot 64 reliably fails with
# "could not get post capella payload header: attempted to wrap nil object" here while the
# all-non-stateless run crossed cleanly, --stateless is causal. If it also crosses cleanly, the
# earlier miss was coincidental (parent-state/proposer draw), not the flag.
participants:
  - el_type: ethrex
    el_image: ethpandaops/ethrex:glamsterdam-devnet-4
    el_extra_params:
      - --http.api=eth,net,web3,admin
    cl_type: prysm
    cl_image: gcr.io/offchainlabs/prysm/beacon-chain:latest
    vc_image: gcr.io/offchainlabs/prysm/validator:latest
    supernode: true
    count: 2
    cl_extra_params:
      - --subscribe-all-subnets
      - --verbosity=debug
    vc_extra_params:
      - --verbosity=debug

  - el_type: ethrex
    el_image: ethpandaops/ethrex:glamsterdam-devnet-4
    el_extra_params:
      - --http.api=eth,net,web3,admin
    cl_type: prysm
    cl_image: gcr.io/offchainlabs/prysm/beacon-chain:latest
    vc_image: gcr.io/offchainlabs/prysm/validator:latest
    validator_count: 63
    cl_extra_params:
      - --verbosity=debug
    vc_extra_params:
      - --stateless
      - --verbosity=debug

network_params:
  fulu_fork_epoch: 0
  gloas_fork_epoch: 2
  seconds_per_slot: 6
  genesis_delay: 40

additional_services:
  - dora
  - spamoor

spamoor_params:
  spammers:
    - scenario: eoatx
      config:
        throughput: 10
    - scenario: blobs
      config:
        throughput: 2

global_log_level: debug

Which issues(s) does this PR fix?

Fixes #

Other notes for review

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description with sufficient context for reviewers to understand this PR.
• I have tested that my changes work as expected and I added a testing plan to the PR description (if applicable).

[syjn99]

Already had a couple of review rounds, and last commits are more like cosmetic one so LGTM