feat: support deploy in out-of-cluster mode

[hansedong]

This PR has 2 features:

1. I use kubelet-csr-approver for automatic approve node serving certificates. I need it can be deployed in a K8s cluster in an out-of-cluster mode. Therefore, I hope it can support the -kubeconfig flag to specify the kubeconfig file outside the cluster.

2. When I specify kubeconfig flag, if the file does not exist, the program exits without any error message, which is obviously abnormal. The reason is that the logger is not initialized when the logic of ctrl.GetConfigOrDie() is executed, so I refactored part of the code logic in internal/cmd/cmd.go.

Now, it works fine for me with little code changes, and I look forward to receiving some suggestions for modifying this PR, thanks~

[hansedong]

@clementnuss Could you please help review this PR? Thank you.

[clementnuss]

thanks for the PR!

[coveralls]

Pull Request Test Coverage Report for Build 4230668290

• 10 of 12 (83.33%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.4%) to 75.893%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/controller/utils.go	10	12	83.33%

Totals
Change from base Build 4171556544:	0.4%
Covered Lines:	170
Relevant Lines:	224

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💛 - Coveralls