Use support.md instead of direct links to GitHub

[dveeden]

First-time contributors' checklist

• I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

What is changed, added or deleted? (Required)

This is a response to https://github.com/pingcap/docs/pull/13375/files#r1308409173

We do still want users to report issues on GitHub, but for questions we have Slack/Discourse/etc and for bugs we want TiDB Enterprise and TiDB Cloud users to create a support ticket as well.

And for some services we have moved from Zendesk to Jira ServiceDesk.

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)
• v7.4 (TiDB 7.4 versions)
• v7.3 (TiDB 7.3 versions)
• v7.2 (TiDB 7.2 versions)
• v7.1 (TiDB 7.1 versions)
• v7.0 (TiDB 7.0 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:
• 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

[dveeden]

cc @CocaLi

[dveeden]

@ran-huang @Oreoxmt PTAL

[ran-huang]

@dveeden I changed all /support.md to https://docs.pingcap.com/tidb/stable/support on purpose because /support.md doesn't exist in TiDB Cloud documentation. When an SQL statement doc is reused in TiDB Cloud TOC, the link of /support.md leads the users to nowhere (and the ci/tidb-cloud-check will report an error for this).

[dveeden]

@ran-huang ah ok. I've removed my last change. Should be good now.

[Oreoxmt]

Rest LGTM

[ran-huang]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ran-huang

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.3: #14743.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.2: #14744.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #14745.