add collectk subcommand and support collect logs for k8s cluster

[nexustar]

What problem does this PR solve?

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

[codecov-commenter]

Codecov Report

Patch coverage: 34.38% and project coverage change: +0.13% :tada:

Comparison is base (7a82994) 30.05% compared to head (5f4dfdd) 30.18%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #447 +/- ## ========================================== + Coverage 30.05% 30.18% +0.13% ========================================== Files 50 52 +2 Lines 4229 4357 +128 ========================================== + Hits 1271 1315 +44 - Misses 2788 2871 +83 - Partials 170 171 +1 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `30.18% <34.38%> (+0.13%)` | :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=pingcap#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files Changed](https://app.codecov.io/gh/pingcap/diag/pull/447?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap) | Coverage Δ | | |---|---|---| | [cmd/diag/command/collect.go](https://app.codecov.io/gh/pingcap/diag/pull/447?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap#diff-Y21kL2RpYWcvY29tbWFuZC9jb2xsZWN0Lmdv) | `33.93% <0.00%> (-0.31%)` | :arrow_down: | | [cmd/diag/command/collectdm.go](https://app.codecov.io/gh/pingcap/diag/pull/447?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap#diff-Y21kL2RpYWcvY29tbWFuZC9jb2xsZWN0ZG0uZ28=) | `30.48% <0.00%> (-0.29%)` | :arrow_down: | | [cmd/diag/command/util\_metricdump.go](https://app.codecov.io/gh/pingcap/diag/pull/447?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap#diff-Y21kL2RpYWcvY29tbWFuZC91dGlsX21ldHJpY2R1bXAuZ28=) | `36.79% <0.00%> (-0.35%)` | :arrow_down: | | [pkg/utils/portforward.go](https://app.codecov.io/gh/pingcap/diag/pull/447?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap#diff-cGtnL3V0aWxzL3BvcnRmb3J3YXJkLmdv) | `0.00% <0.00%> (ø)` | | | [cmd/diag/command/collectk.go](https://app.codecov.io/gh/pingcap/diag/pull/447?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap#diff-Y21kL2RpYWcvY29tbWFuZC9jb2xsZWN0ay5nbw==) | `46.24% <46.24%> (ø)` | | | [cmd/diag/command/root.go](https://app.codecov.io/gh/pingcap/diag/pull/447?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pingcap#diff-Y21kL2RpYWcvY29tbWFuZC9yb290Lmdv) | `20.09% <100.00%> (+0.38%)` | :arrow_up: |

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