Create a rule template

Creates a personal rule template owned by the caller. Items are validated exactly as machine rules are: source must be any/a built-in source name/a non-negative number, a non-empty event_pattern must be a valid regex (empty means all events), mode must be 1-4, and sanitize_scope must be any/unsanitized/sanitized/conditional/sanitized:<CLASS> (absent defaults to any); a mode 3 item with a sanitize_scope other than any is a 400. name is at most 128 bytes and description at most 512. Maximum 50 templates per user and 200 items per template. Names are unique per owner, case-insensitively. Cookie callers must pass CSRF.

This is a write: a read-only API key is refused with 403.