v7.1.4: Change the default log level of tiflash (#15961)

[ti-chi-bot]

This is an automated cherry-pick of #15961

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What is changed, added or deleted? (Required)

Which TiDB version(s) do your changes apply to? (Required)

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For details, see tips for choosing the affected versions.

• master (the latest development version)
• v7.6 (TiDB 7.6 versions)
• v7.5 (TiDB 7.5 versions)
• v7.4 (TiDB 7.4 versions)
• v7.3 (TiDB 7.3 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)

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

• This PR is translated from: Change the default log level of tiflash docs-cn#15991
• Other reference link(s):

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]

PR needs rebase.

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[Oreoxmt]

/cc @JaySon-Huang

[ti-chi-bot]

@JaySon-Huang: adding LGTM is restricted to approvers and reviewers in OWNERS files.

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[Oreoxmt]

/unhold
/approve

[ti-chi-bot]

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