refactor yurtctl init

[Peeknut]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage
/sig storage

/kind feature

What this PR does / why we need it:

Use sealer to init the cluster which is more user-friendly.
In addition, we can remove the dependency of k8s.io/kubernetes in yurtctl init.

Which issue(s) this PR fixes:

Fixes #672

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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In response to this:

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage
/sig storage

/kind feature

What this PR does / why we need it:

Use sealer to init the cluster which is more user-friendly.
In addition, we can remove the dependency of k8s.io/kubernetes in yurtctl init.

Which issue(s) this PR fixes:

Fixes #672

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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[Peeknut]

@rambohe-ch PTAL
The local test passed. And the cluster image needs to be uploaded to the registry.

[rambohe-ch]

@Peeknut Maybe the readme of yurtctl init should be updated.

[Peeknut]

@Peeknut Maybe the readme of yurtctl init should be updated.

done

[rambohe-ch]

/lgtm
/approve

[openyurt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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