Add comment about beacon node config

apis/eventstream/index.yaml

@@ -115,6 +115,10 @@ get:
                    `execution-apis` with two differences: 1) `snake_case` identifiers must be used
                    rather than `camelCase`; 2) integers must be encoded as quoted decimals rather
                    than big-endian hex.
+
+                The frequency at which this event is sent may depend on beacon node configuration.
+                The fee recipient may also be set via beacon node config, but should likely be
+                ignored by block builders and most other API consumers.
               value: |
                 event: payload_attributes
                 data: {"version": "capella", "data": {"proposer_index": "123", "proposal_slot": "10", "proposal_block_number": "9", "parent_block_root": "0xcf8e0d4e9587369b2301d0790347320302cc0943d5a1884560367e8208d920f2", "parent_block_hash": "0x9a2fefd2fdb57f74993c7780ea5b9030d2897b615b89f808011ca5aebed54eaf", "payload_attributes": {"timestamp": "123456", "prev_randao": "0xcf8e0d4e9587369b2301d0790347320302cc0943d5a1884560367e8208d920f2", "suggested_fee_recipient": "0x0000000000000000000000000000000000000000", "withdrawals": [{"index": "5", "validator_index": "10", "address": "0x0000000000000000000000000000000000000000", "amount": "15640"}]}}},