Add auth_socket support

[dveeden]

What is changed, added or deleted? (Required)

Add Socket Authentication info.

Note that this doesn't update default_authentication_plugin as setting that to auth_socket doesn't make sense and isn't supported.

Also adding info about FIDO authentication that was released in MySQL 8.0.27 this week.

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

• master (the latest development version)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)
• v4.0 (TiDB 4.0 versions)
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

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

Related PR: pingcap/tidb#27561

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:

• TomShawn
• morgo

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[dveeden]

If there are more things from 8.0.27 like MFA for which we want to document compatibility we should probably do that in a separate PR.

[shichun-0415]

@s3nt3. PTAL. Thanks.

[s3nt3]

LGTM

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: 3da7b11