<!-- Audit Event documentation: See https://docs.gitlab.com/ee/administration/audit_events.html --> ## Audit need <!-- Describe the real-world use case for the audit event you want to introduce, and explain the closest thing that GitLab already captures. --> When custom HTTP headers are added, removed, or changed for streaming audit events, this is a sensitive change that should be recorded. ## Proposal <!-- Describe the audit event you are proposing should be added, including any details of what should be captured, how, and why. --> Create a new audit event when the following occurs: * Custom HTTP header is _added_ for streaming audit events * Custom HTTP header is _removed_ for streaming audit events * Custom HTTP header is _updated_ for streaming audit events Note: Include the key of the key/value pair in the description of the event but omit the value. There are potentially sensitive API keys in those pairs we do not want to expose. Ensure that new event names are created, used, and documented for this event as needed.