Document conditional put support as part of S3 API compat

[Frederik-Baetens]

Summary

AWS implemented this for PutObject after we did, which is why it was in the extensions section. Now that AWS has implemented this, we can move it into the regular S3 api document, instead of the extensions document.

S3 implements this now, so we can just check it off as a standard operation.

Documentation checklist

• The change adheres to the documentation style guide.

[github-actions]

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[cloudflare-docs-bot]

Review

⚠️ 3 warnings found in commit 8440dd3.

Warnings (3)

File	Issue
r2/api/s3/api.mdx line 139	Escape angle brackets in MDX prose — Line adds unescaped < in prose: | ✅ [PutObject](https://docs.aws.amazon.com/AmazonS3/latest/API/API_PutObject.html) | ✅ Conditional Operations: <br/>   ✅ If-Match <br/>   ✅ If-Modified-Since <br/>   ✅ If-None-Match <br/>   ✅ If-Unmodified-Since <br/> ✅ System Metadata: <br/>   ✅ Content-Type <br/>   ✅ Cache-Control <br/>   ✅ Content-Disposition <br/>   ✅ Content-Encoding <br/>   ✅ Content-Language <br/>   ✅ Expires <br/>   ✅ Content-MD5 <br/> ✅ Storage Class: <br/>   ✅ x-amz-storage-class <br/>     ✅ STANDARD <br/>     ✅ STANDARD_IA <br/> ❌ Object Lifecycle <br/> ❌ Website: <br/>   ❌ x-amz-website-redirect-location <br/> ❌ SSE: <br/>   ❌ x-amz-server-side-encryption-aws-kms-key-id <br/>   ❌ x-amz-server-side-encryption <br/>   ❌ x-amz-server-side-encryption-context <br/>   ❌ x-amz-server-side-encryption-bucket-key-enabled <br/> ✅ SSE-C: <br/>   ✅ x-amz-server-side-encryption-customer-algorithm <br/>   ✅ x-amz-server-side-encryption-customer-key <br/>   ✅ x-amz-server-side-encryption-customer-key-MD5 <br/> ❌ Request Payer: <br/>   ❌ x-amz-request-payer <br/> ❌ Tagging: <br/>   ❌ x-amz-tagging <br/> ❌ Object Locking: <br/>   ❌ x-amz-object-lock-mode <br/>   ❌ x-amz-object-lock-retain-until-date <br/>   ❌ x-amz-object-lock-legal-hold <br/> ❌ ACL: <br/>   ❌ x-amz-acl <br/>   ❌ x-amz-grant-full-control <br/>   ❌ x-amz-grant-read <br/>   ❌ x-amz-grant-read-acp <br/>   ❌ x-amz-grant-write-acp <br/> ❌ Bucket Owner: <br/>   ❌ x-amz-expected-bucket-owner | Fix: Replace < with &lt; or wrap the text in backticks.
r2/api/s3/api.mdx line 140	Escape angle brackets in MDX prose — Line adds unescaped < in prose: | ✅ [DeleteObject](https://docs.aws.amazon.com/AmazonS3/latest/API/API_DeleteObject.html) | ❌ Multi-factor authentication: <br/>   ❌ x-amz-mfa <br/> ❌ Object Locking: <br/>   ❌ x-amz-bypass-governance-retention <br/> ❌ Request Payer: <br/>   ❌ x-amz-request-payer <br/> ❌ Bucket Owner: <br/>   ❌ x-amz-expected-bucket-owner | Fix: Replace < with &lt; or wrap the text in backticks.
r2/api/s3/api.mdx line 167	Escape angle brackets in MDX prose — Line adds unescaped > in prose: </Details> Fix: Replace > with &gt; or wrap the text in backticks.

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