gracedb-2.27.1

pre-O4b bug fixes and performance improvements:

• enable x-ray segments for user management tools (!204 (merged))
• Missing else clause in check_and_serve_file (#343 (closed))
• Add SSM label (575308b4)
• Fix outdated documentation (cba89ba1, ab8cea28)
• voevent and table changes for cwb-bbh (!210 (closed))