fix: resolve Service Catalog portfolio sharing race condition

[jtaylortech]

Issue, #601

This PR fixes the InvalidStateException errors that occur when sharing Service Catalog portfolios with multiple organizational units.

Problem:
The existing implementation uses a random delay to prevent concurrent portfolio share operations, which is unreliable and still results in failures when multiple OUs are targeted. When failures occur, the lambda returns SUCCESS to CloudFormation despite the error, causing silent failures.

Solution:
This PR implements two complementary approaches as suggested in the issue:

1. Sequential Processing via CDK Dependencies:

   • Modified share-portfolio-with-org.ts to add CloudFormation dependencies between portfolio share resources
   • Ensures portfolio shares are created one at a time, preventing concurrent operations
   • This is the primary fix that prevents the race condition at the orchestration level

2. Retry Logic for InvalidStateException:

   • Added exponential backoff retry mechanism (up to 5 attempts) in createPortfolioShare(), updatePortfolioShare(), and deletePortfolioShare() functions
   • Specifically catches InvalidStateException and retries with increasing delays (2s, 4s, 8s, 10s, 10s)
   • Provides resilience if race conditions still occur despite sequential processing
   • Maintains existing error handling for other exception types

Changes:

• share-portfolio-with-org.ts: Added resource dependencies to enforce sequential creation
• share-portfolio-with-org/index.ts:
  • Removed unreliable random delay
  • Added retry logic with exponential backoff for InvalidStateException
  • Improved error messages for debugging

Testing:

• Code compiles without TypeScript errors
• Maintains backward compatibility
• Error handling paths are preserved

Benefits:

• Eliminates race condition failures when sharing with multiple OUs
• More reliable than random delays
• Better observability with retry attempt logging
• No need to manually deploy customizations stack multiple times

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.