chore(batch): undeprecate useOptimalInstanceClasses property

[badmintoncryer]

Issue # (if applicable)

Closes #36291.

Reason for this change

The useOptimalInstanceClasses property was deprecated in v2.220 in favor of defaultInstanceClasses, but there is no way to exclude the optimal instance type using defaultInstanceClasses alone. Users who want to specify only custom instance types (e.g., R4 only) without optimal being automatically added have no non-deprecated path forward.

Setting defaultInstanceClasses: [] (empty array) does not prevent optimal from being added because the current logic treats an empty array the same as undefined.

Description of changes

• Removed @deprecated annotation from useOptimalInstanceClasses property
• Updated README to remove the deprecation warning and reorganized the "Choosing Your Instance Types" section with:
  • Clear subsections for each use case (Default Instance Classes, Specific Instance Types Only, Optimal Instance Classes)
  • A configuration reference table for quick lookup
  • Example showing how to use useOptimalInstanceClasses: false to exclude optimal

Alternatives considered

Three options were discussed in #36291:

1. Remove deprecation (this PR) - Restores useOptimalInstanceClasses as a non-deprecated property
2. Treat empty defaultInstanceClasses: [] as "exclude all defaults" - Would introduces implicit behavior
3. Change default behavior - Breaking change, not acceptable

Option 1 was chosen because:

• Minimal code change (documentation only)
• No risk of breaking existing users
• useOptimalInstanceClasses provides explicit, clear control that defaultInstanceClasses cannot fully replace

Describe any new or updated permissions being added

N/A

Description of how you validated changes

Existing tests

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[github-actions]

	Tests	Passed ❌️	Skipped	Failed
Security Guardian Results

Test	Result
No test annotations available

• View Security Guardian Results

[github-actions]

	Tests	Passed ❌️	Skipped	Failed
Security Guardian Results with resolved templates

Test	Result
No test annotations available

• View Security Guardian Results with resolved templates