Add description for --log-file parameter

[fengou1]

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What is changed, added or deleted? (Required)

Add description for --log-file parameter, --log-file="-" use to print log to stdout

the --log-file="-" used by DBaaS, however, no doc described what does it mean.

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• master (the latest development version)
• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
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What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s): lightning: setting --log-file "-" will not print any log to stdout tidb#29876

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• 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:

• Liuxiaozhen12
• hfxsd

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[Liuxiaozhen12]

/merge

[ti-chi-bot]

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

Commit hash: 6eea302

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #7615.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #7616.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #7617.