feat: add agentcore destroy command

[huanshenyi]

Description

Brief description of changes

Type of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Testing

• Unit tests pass locally
• Integration tests pass (if applicable)
• Test coverage remains above 80%
• Manual testing completed

Checklist

• My code follows the project's style guidelines (ruff/pre-commit)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Security Checklist

• No hardcoded secrets or credentials

• No new security warnings from bandit

• Dependencies are from trusted sources

• No sensitive data logged

  Breaking Changes

  N/A - This is an additive feature that doesn't modify existing functionality.

  Additional Notes

  New Command Usage

  agentcore destroy                    # Destroy default agent (with confirmation)
  agentcore destroy --agent my-agent  # Destroy specific agent
  agentcore destroy --dry-run         # Preview what would be destroyed
  agentcore destroy --force           # Skip confirmation prompts
  
  Resources Cleaned Up
  
  - Bedrock AgentCore endpoints
  - Bedrock AgentCore agent runtimes
  - ECR images (latest tag only for safety)
  - CodeBuild projects
  - IAM execution roles (only if not used by other agents)
  - Agent deployment configuration
  
  Safety Features
  
  - Confirmation prompts by default
  - Dry-run mode to preview changes
  - Shared resource protection (won't delete IAM roles used by multiple agents)
  - Comprehensive error handling and logging
  - Graceful handling of already-deleted resources
  
  Test Coverage
  
  - 25+ comprehensive unit tests covering all scenarios
  - CLI integration tests
  - Error handling and edge case testing
  - Mock-based testing for AWS service interactions