dm: add description about mysql-instance.meta

[shichun-0415]

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What is the related PR or file link(s)?

• This PR is translated from: dm: add description about mysql-instance.meta docs-cn#11790
• Other reference link(s):

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• Delete files
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• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• GMHDBJD
• qiancai

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[GMHDBJD]

LGTM

[shichun-0415]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 1768cf8