[WIP] Add Context to Run method of the manager

[afritzler]

What this PR does / why we need it:

Motivation

Running the MCM as a provider makes it currently hard to test because there is no clean way to terminate a running MCM instance via a signal/context cancel.

Proposed change

This PR introduces a context handler to the run() method of the manager. You can now pass a context e.g. SignalHandler

if err := app.Run(ctrl.SetupSignalHandler(), s); err != nil {
	fmt.Fprintf(os.Stderr, "%v\n", err)
	os.Exit(1)
}

This is a BREAKING change for all provider implementer as they now have to pass on a context.

Additionally a few potential nil pointer derefs have been fixed an a couple of linting issues addressed.

Release note:

Add Context to Run method of the manager

[gardener-robot]

@afritzler Thank you for your contribution.

[gardener-robot]

@afritzler You need rebase this pull request with latest master branch. Please check.

[himanshu-kun]

@afritzler we have a planned refactoring for MCM where we will add signal handling. Unless you think that there is a blocker in consuming/testing MCM due to this issue, we would like to ask you to close this PR , in favour the aforementioned issue.