Refactor client handling

[cbarbian-sap]

This PR has two purposes:

First, a step towards the standard 'errors' package is made. That is, any references to utilerrors.NewAggregate() and multierror.Append() are replaced by errors.Join(). Note that errors produced by errors.Join() support both errors.Is() and errors.As().
Furthermore, all imports of the deprecated 'github.com/pkg/errors' package are aliased as 'legacyerrors'. The only remaining usage of 'legacyerrors' should be legacyerrors.Wrap() and legacyerrors.Wrapf(). In a later phase, we will replace these by fmt.Errorf() with %w.

Second, the K8s client handling in component.Reconcile() is revisited. That is, instead of using the manager's client (i.e. mgr.GetClient()) for the component reconciler (that is the client interacting with the component resources), we construct a dedicated client from mgr.GetConfig() and mgr.GetScheme(). Notes:

• the manager's scheme is still required to recognize the component's group and the corev1 group
• the constructed clients will emit our metrics (which was not the case before)
• hooks and implementations of component.Reference[T] still use the manager's client.

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