feat(organizations): add comprehensive organization management resources

[ggiallo28]

Implement three new Terraform resources for managing LiteLLM organizations:

• litellm_organization: Full organization CRUD with budget controls
• litellm_organization_member: Single member management
• litellm_organization_member_add: Bulk member operations

Features:

• Complete CRUD operations for all resources
• Budget and rate limiting controls (max_budget, tpm_limit, rpm_limit)
• Role-based access control (org_admin, internal_user, internal_user_viewer)
• Comprehensive acceptance test coverage with 100% pass rate
• Automated test infrastructure using docker-compose

Implementation Details:

• Added 6 new client methods for organization and member operations
• Fixed HTTP method usage (DELETE for delete operations, not POST)
• Created test infrastructure with automatic user creation
• Added proper error handling for existing users
• Integrated official LiteLLM docker-compose for testing

Test Results:

• All 5 acceptance tests passing
• Test execution time: ~4 seconds
• Automated setup and teardown via Makefile

Files Changed:

• 7 new files (3 resources + 3 tests + provider_test.go)
• 6 modified files (client, provider, types, Makefile, go.mod, go.sum)
• Total: 1,023 insertions(+), 9 deletions(-)

Breaking Changes: None

BREAKING CHANGE: None