fix(elasticloadbalancingv2): allow logging in env-agnostic stacks

[Dricmoy]

Issue # (if applicable)

Closes #27432.

Reason for this change

ELBv2 access logging currently requires a resolved stack region because CDK looks up a legacy, region-specific Elastic Load Balancing account principal before synthesizing the bucket policy. That prevents access logging from being used in environment-agnostic stacks even though the current Elastic Load Balancing documentation recommends the service principal logdelivery.elasticloadbalancing.amazonaws.com.

Description of changes

• Uses the Elastic Load Balancing log delivery service principal when the stack region is unresolved.
• Preserves the existing region-specific account principal behavior for concrete regions where CDK has legacy ELBv2 account metadata.
• Removes stale documentation that said access logging and connection logging cannot be used in environment-agnostic stacks.
• Adds ALB and NLB coverage for environment-agnostic access logging, plus ALB connection logging coverage.

Describe any new or updated permissions being added

For environment-agnostic ELBv2 logging bucket policies, CDK now synthesizes an s3:PutObject grant to the logdelivery.elasticloadbalancing.amazonaws.com service principal instead of throwing during synthesis. Concrete-region behavior is unchanged.

Description of how you validated changes

• env PATH=/opt/homebrew/opt/node@24/bin:$PATH yarn test --coverage=false --runTestsByPath aws-elasticloadbalancingv2/test/alb/load-balancer.test.ts aws-elasticloadbalancingv2/test/nlb/load-balancer.test.ts
• env PATH=/opt/homebrew/opt/node@24/bin:$PATH yarn build --skip-lint

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES
• My change includes tests
• I have updated documentation where necessary

[aws-cdk-automation]

(This review is outdated)

✅ Updated pull request passes all PRLinter validations. Dismissing previous PRLinter review.