add retrying k8s client implementation

[Diaphteiros]

What this PR does / why we need it:
Adds a client.Client implementation that can be configured to retry operations multiple times instead of returning an error on the first unsuccessful attempt.

Which issue(s) this PR fixes:
Required for openmcp-project/openmcp-operator#67

Special notes for your reviewer:
Factored out of #66

Release note:

Added a `pkg/retry` package that contains a `client.Client` implementation which retries failed k8s operations according to configurable parameters (interval, max number of attempts, timeout, interval backoff multiplier).