Add tracing

Add tracing

- add otel dependencies [0]
- register otel middleware on router
- use grpc trace exporter
- this also updates gorilla/mux (1.7.3 -> 1.8.0)
- exporter configuration is available via
  environment variables [1]

[0] v1.2.0 of otel dependencies is used due to a dependency
    on v1 of github.com/go-logr/logr in later versions.
    The update from v0 to v1 of that dependency would require
    updating all the k8s.io packages from v0.19 -> v0.21 too.
[1] https://opentelemetry.io/docs/languages/sdk-configuration/otlp-exporter/

Issue-ID: MULTICLOUD-1535
Change-Id: I0cdd9f1682542e96b8808e59f9b83868ab2d8565
Signed-off-by: Fiete Ostkamp <fiete.ostkamp@telekom.de>