net/traefik: Update to upstream release 2.7.1

Details:

• Buxfix and documentation improvements, https://github.com/traefik/traefik/releases/tag/v2.7.1
• No known breaking configuration changes: https://doc.traefik.io/traefik/migration/v2/

MFH: 2022Q2
(cherry picked from commit 505cc55fdc65402c124754c04dd4a96ff628dc39)