shardddl: add unlock ddl lock doc for optimistic mode

[lichunzhu]

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)

DM optimistic mode has support shard-ddl-lock in v6.0. This PR will update the related documents.

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 (in Chinese).

• master (the latest development version)
• v6.0 (TiDB 6.0 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)
• 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)?

• This PR is translated from:
• Other reference link(s): Optimistic: support unlock-ddl-lock for Optimistic Sharding DDL tiflow#4087

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:

• GMHDBJD

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[lichunzhu]

@GMHDBJD @TomShawn PTAL

[TomShawn]

@GMHDBJD @TomShawn PTAL

Is there an FD JIRA for this? I think this is expected to be tracked in JIRA and triaged by Cira and QA.

[GMHDBJD]

LGTM

[ran-huang]

这里建议用 <SimpleTab> 来分别显示悲观模式和乐观模式

[lichunzhu]

Is this fix correct?298fff8

[ran-huang]

改成了这样：3e398cf

官网会渲染为类似这样的效果：

[ran-huang]

/verify

[ran-huang]

@lichunzhu @GMHDBJD PTAL at this commit cc2a426. The rest of the PR LGTM.

[qiancai]

Removed the needs-cherry-pick-release-6.6 label because the v6.6 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v6.6 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-7.0 label because the v7.0 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v7.0 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-7.2 label because the v7.2 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v7.2 and will no longer receive new updates.