Ignore unavailable deployments and handle kubeconfig secret rotation

[ashwani2k]

What this PR does / why we need it:
This PR handles skipping the scaling operation for deployment when they are not available in the cluster.
The logs are also refined to avoid noise and clutter.
It also handled the bug introduced with reloading of shoot kubeconfig as reported with #36.

Which issue(s) this PR fixes:
Fixes #40 #36

Special notes for your reviewer:

1. The PR upgrades GO dependency to 1.17
2. There is also a delay introduced before checking dependents for desire availability. This is introduced as checking for availability immediately after scaling operation always failed as it takes some time for the deployment to become ready.
   Currently it is a hacky way with 2 sec delay as per what was observed from the tests.
   Without this delay also the scaling operation happens but it is honored in the next reconciliation cycle. This creates an overall delay of 30s scaling delay per deployment requiring scaling.
3. In order to handle the kubeconfig rotation race condition where for some edge case the probe fails to access the latest kubeconfig and continues to fail unless restated. A retry mechanism is introduced which shall update the secret. The retry only acts if the error api errors of
4. Refactors the error handling for probe.
5. Updated alpine image to 3.15

Release note:

A bug is fixed which allowed dependency-watchdog to not ignore scaling operations on deployment which are not enabled/deployed in a given cluster
A bug with uploading of a rotated dependency-watchdog-probe secrets is now fixed by refreshing the clients with updated secrets. 

[ashwani2k]

@unmarshall -- As suggested by you, I've introduced a retry mechanism to handle the kubeconfig rotation scenario. Also refined the logs overall and made them leaner for happy path. Moved some of the logs to Level 5.
Kindly have a look at the commit 38437b4

[unmarshall]

Added comments

[ashwani2k]

Thanks Madhav, I agree we can make a total separation of concerns.
The changes are made with the commit 15f476a and it also tested on a local seed/shoot setup.

[ashwani2k]

Fixed test errors with missing arguments https://github.com/gardener/dependency-watchdog/compare/15f476af3a05b03b7922b3866cf2a46df1687c51..1d5b24b617cefdf54bef6493eddbec22aecf9108

[unmarshall]

/lgtm