fix(operator): Support private VPC S3 endpoints in endpoint validation

[ptux]

Summary

• Add regex-based validation for AWS VPC S3 endpoints (https://vpce-{id}.s3.{region}.vpce.amazonaws.com) to validateS3Endpoint()
• Reject bucket-prefixed endpoints to prevent unintended folder creation in S3 buckets
• Provide specific error messages for region mismatches and invalid formats

Context

This is a clean rewrite of #19247 (originally by @puretension with review contributions from @JoaoBraveCoding) which had been open for 9 months. The original PR had a test bug (expected scheme-prefixed endpoint in ForcePathStyle test while extractS3ConfigSecret strips the scheme) and accumulated 11 commits including merge commits.

This PR squashes everything into a single commit with the test bug fixed.

Fixes #19243

Changes

operator/internal/handlers/internal/storage/secrets.go:

• Add compiled regex patterns for standard S3, VPC, and bucket-prefixed endpoint formats
• Rewrite validateS3Endpoint() to validate using regex matching with region extraction
• Add errS3EndpointAWSNoRegion and errS3EndpointNoBucketName error variables

operator/internal/handlers/internal/storage/secrets_test.go:

• Add test cases: valid VPC endpoint, bucket-prefixed VPC endpoint rejection, wrong region VPC endpoint
• Add ForcePathStyle test for VPC endpoints verifying ForcePathStyle=false
• Update existing error message assertions to match new validation output

Test plan

• go test ./internal/handlers/internal/storage/... passes (all TestS3Extract* tests)
• CI checks pass

Co-authored-by: puretension rlrlfhtm5@gmail.com
Co-authored-by: JoaoBraveCoding joao.coding@gmail.com

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