CEL Interceptor: Filter & Modify Event Payloads with CEL Expressions

The example overlays definition below adds two new fields to the event payload: \n\n\text{extensions:\n truncated_sha: <truncated_sha_value>\n branch_name: <branch_name_value>}\n\nThese fields, "truncated_sha" and "branch_name", are included in the extensions field of the event payload. The values for these fields can be provided by the CEL Interceptor based on the incoming event or any other logic defined in the CEL expression.