revert: cleanup sqlgram

[Oreoxmt]

What is changed, added or deleted? (Required)

Revert #16049.

After removing media/sqlgram from the master branch, docs in other branches that use the image from media/sqlgram fails to render. For example https://docs.pingcap.com/tidb/stable/sql-statement-use:

https://docs-archive.pingcap.com/tidb/v2.1/sql-statement-begin:

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Do your changes match any of the following descriptions?

• Delete files
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• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[Oreoxmt]

/cc @dveeden @qiancai

[dveeden]

I assume this is a temporary solution?

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-04-07 07:53:07.732654817 +0000 UTC m=+776049.260195361: ☑️ agreed by qiancai.
• 2024-04-07 08:19:12.104106704 +0000 UTC m=+777613.631647250: ☑️ agreed by dveeden.

[Oreoxmt]

@dveeden To optimize the storage and costs for our CDN while reusing images across multiple versions, we currently "merge" all images under media/ across all branches and upload them to https://download.pingcap.com/images/docs/. This means we keep only one copy each image instead of one per branch. With 25 versions of TiDB docs in total, this approach saves significant storage space and costs. In most cases, we want to reuse images across versions to ensure consistency. Therefore, we cannot delete any images unless they are unused across all branches.

[Oreoxmt]

/approve

[ti-chi-bot]

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