Bug fixes:
- [api] Do not create observability model by default (#11476 by rtribotte)
- [fastproxy] Fix content-length header assertion (#11498 by kevinpollet)
- [fastproxy] Handle responses without content length header (#11458 by rtribotte)
- [k8s/crd,k8s] Add missing headerField in Middleware CRD (#11499 by jspdown)
- [tracing,accesslogs] Bring back TraceID and SpanID fields in access logs (#11450 by rtribotte)
Misc: