feat: add utility functions for scheduler

[Diaphteiros]

What this PR does / why we need it:
When implementing preemptive scheduling, I needed a few utility functions which I put into this repo.
See release notes for more details.

Which issue(s) this PR fixes:
None

Special notes for your reviewer:
Prerequisite for openmcp-project/openmcp-operator#67

Release note:

The `pkg/collections/maps` package now has `MapKeys`, `MapValues`, and `GetAny` functions to extract data from maps.

The `pkg/collections` package now has projection (`ProjectSlice`, `ProjectMapToSlice`, `ProjectMapToMap`) and aggregation (`AggregateSlice`, `AggregateMap`) functions to perform operations for each entry of a slice or map.

The `pkg/controller` package has a new `RemoveFinalizerWithPrefix` function that removes the first finalizer from the object with the given prefix.

The testing library's `ComplexEnvironment` and `Environment` types can now be configured to add UIDs to created resources (the fake client doesn't do this). Use the `WithUIDs` method in the builder and additionally use `InjectUIDOnObjectCreation` if you overwrite the fake client's interceptor funcs to enable this functionality.

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).