Traefik - v2.6.6

Bug fixes:
- [acme] Fix RenewInterval computation in ACME provider (#8969 by smasset-orange)
- [ecs,logs] Remove duplicate error logs (#8916 by rtribotte)
- [ecs] Filter out ECS anywhere instance IDs (#8973 by JohnPreston)
- [middleware] Re-add missing writeheader call in flush (#8957 by mpl)
- [middleware] Fix bug for when custom page is large enough (#8932 by mpl)
- [middleware] Fix regexp handling in redirect middleware (#8920 by tomMoulard)
- [plugins] Update Yaegi to v0.11.3 (#8954 by kevinpollet)

Documentation:
- [k8s/gatewayapi] Fix certificateRefs in dynamic configuration (#8940 by kahirokunn)
- [logs] Move accessLog.fields example to TOML section (#8944 by major)
- [logs] Add default mode for fields.names to access log (#8933 by aleksvujic)
- [middleware] Fix default for buffering middleware (#8945 by rtribotte)
- [middleware] Preflight requests are not forwarded to services (#8923 by sizief)
- Add title and description metadata to documentation pages (#8941 by ldez)
- Update dynamic and static configuration references (#8918 by ldez)