Use support.md instead of direct links to GitHub (#14648)

[ti-chi-bot]

This is an automated cherry-pick of #14648

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

[ran-huang]

/approve

[ti-chi-bot]

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

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