improve csr approver controller by replacing kubernetes client with client.Client

[rambohe-ch]

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

/kind enhancement

What this PR does / why we need it:

in controller-runtime v0.16, client.Client is supported to update csr approval. so remove original kubernetes client in csr approver controller and use the client.Client to replace it.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.1% Duplication on New Code

See analysis details on SonarCloud

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 56.01%. Comparing base (e42545e) to head (6687587).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2058 +/- ## ========================================== + Coverage 55.53% 56.01% +0.48% ========================================== Files 186 186 Lines 18088 18082 -6 ========================================== + Hits 10045 10129 +84 + Misses 7013 6920 -93 - Partials 1030 1033 +3 ``` | [Flag](https://app.codecov.io/gh/openyurtio/openyurt/pull/2058/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openyurtio) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/openyurtio/openyurt/pull/2058/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openyurtio) | `56.01% <100.00%> (+0.48%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=openyurtio#carryforward-flags-in-the-pull-request-comment) to find out more.

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