Update CHANGELOG

[lucassaldanha]

Note

Update CHANGELOG with a breaking config export removal and several additions (User-Agent header, gas limit increase, metric updates, Get Blobs API).

• Changelog (Unreleased):
  • Breaking: Stop exporting GOSSIP_MAX_SIZE, MAX_CHUNK_SIZE, TTFB_TIMEOUT, RESP_TIMEOUT; note compatibility with fulu-compliant releases.
  • Additions/Improvements:
    • Add User-Agent header (Validator Client identifier/version).
    • Raise default validator registration gas limit to 60M across networks.
    • Rename metric for data_column_sidecar_by_root RPC to network_rpc_data_column_sidecars_by_root_requested_sidecars_total.
    • Add peer-count-per-topic metric for data_column_sidecar subnet.
    • Add Beacon API GET /eth/v1/beacon/blobs/{block_id} (Get Blobs).

^{Written by Cursor Bugbot for commit 4e7dac7. This will update automatically on new commits. Configure here.}