feat(rds): add standalone resource creation for ParameterGroup

[gudipati]

Issue # (if applicable)

Closes #9741

Reason for this change

Since #8959, ParameterGroup uses a lazy creation pattern where CloudFormation resources are only generated when the parameter group is bound to an instance or cluster (either explicitly via bindToInstance()/bindToCluster() or implicitly when passed to a DatabaseInstance/DatabaseCluster).

This change adds an explicit static methods ParameterGroup.forInstance() / ParameterGroup.forCluster() that allows users to create standalone parameter groups while maintaining the lazy instantiation pattern and backward compatibility.

Description of changes

Added two static factory methods to the ParameterGroup class similar to SingletonPolicy.forRole():

• ParameterGroup.forInstance(): Creates a standalone instance parameter group (AWS::RDS::DBParameterGroup)
• ParameterGroup.forCluster(): Creates a standalone cluster parameter group (AWS::RDS::DBClusterParameterGroup)

Describe any new or updated permissions being added

N/A

Description of how you validated changes

Validated with new unit-tests and integ test

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
Please try merge from main to avoid findings unrelated to the PR.

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	Tests	Passed ✅	Skipped	Failed
Security Guardian Results	48 ran	48 passed

Test	Result
No test annotations available

• View Security Guardian Results

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
Please try merge from main to avoid findings unrelated to the PR.

---

	Tests	Passed ✅	Skipped	Failed
Security Guardian Results with resolved templates	48 ran	48 passed

Test	Result
No test annotations available

• View Security Guardian Results with resolved templates

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-03-18 10:37 UTC · Rule: default-squash
• ✅ Checks passed · in-place
• ✅ Merged — 2026-03-18 11:21 UTC · at cffd0fbe76a41c4c3ed57b600ddeeaeedb52d213

This pull request spent 43 minutes 53 seconds in the queue, including 43 minutes 30 seconds running CI.

Required conditions to merge

• #approved-reviews-by >= 1 [🛡 GitHub branch protection]
  • feat(rds): add standalone resource creation for ParameterGroup #37165
• #changes-requested-reviews-by = 0 [🛡 GitHub branch protection]
  • feat(rds): add standalone resource creation for ParameterGroup #37165
• any of [🛡 GitHub branch protection]:
  • check-success = validate-pr
  • check-neutral = validate-pr
  • check-skipped = validate-pr
• any of [🛡 GitHub branch protection]:
  • check-success = build
  • check-neutral = build
  • check-skipped = build

[mergify]

Thank you for contributing! Your pull request will be updated from main and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[github-actions]

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