support: replace internals.tidb.io with discussions on GitHub

[qiancai]

What is changed, added or deleted? (Required)

internals.tidb.io is now inaccessible. The alternative option is https://github.com/orgs/pingcap/discussions.

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

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 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)

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

• This PR is translated from: support: replace internals.tidb.io with discussions on GitHub docs#20294
• 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]

[LGTM Timeline notifier]

Timeline:

• 2025-02-14 07:27:22.459860546 +0000 UTC m=+600684.856082609: ☑️ agreed by Oreoxmt.

[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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• OWNERS [qiancai]

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #19836.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #19837.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #19838.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.3: #19839.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #19840.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.4: #19841.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #19842.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #19843.