[app] Fix Shutdown Logic

[ricoberger]

We forgot to shutdown the created tracer provider. This is now
implemented, by returning a client in the tracer setup. This client
exposes a Shutdown method which can be used to gracefully shutdown the
tracer provider.

We also fixed the context timeouts for all http server, so that the hub,
satellite and app server are having a timeout of 30 seconds and the
metrics server has a timeout of 10 seconds as it is also used for the
tracer client.

This way we always stay within the 90 seconds timeout, which was
configured at the Kubernetes deployments for the hub and satellite.

• I added a CHANGELOG entry for this change.
• I adjusted the corresponding documentation for this change.
• I adjusted the values.yaml file and the documentation for all values.

[codecov-commenter]

Codecov Report

Merging #396 (2ae909e) into main (a8a71d8) will decrease coverage by 0.07%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #396      +/-   ##
==========================================
- Coverage   45.43%   45.35%   -0.08%     
==========================================
  Files         134      134              
  Lines       10435    10452      +17     
==========================================
  Hits         4741     4741              
- Misses       5614     5631      +17     
  Partials       80       80              

Impacted Files	Coverage Δ
cmd/kobs/hub/hub.go	0.00% <0.00%> (ø)
cmd/kobs/satellite/satellite.go	0.00% <0.00%> (ø)
pkg/app/app.go	0.00% <0.00%> (ø)
pkg/hub/hub.go	0.00% <0.00%> (ø)
pkg/metrics/metrics.go	0.00% <0.00%> (ø)
pkg/satellite/satellite.go	0.00% <0.00%> (ø)
pkg/tracer/tracer.go	0.00% <0.00%> (ø)

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