Add API key environment variable support for conversation components

[bibryam]

Description:
Following the successful implementation of centralized model environment variables (PR #3792), we should implement the same pattern for API keys to provide consistent runtime configuration across all conversation components.

Proposed Enhancement:
Add API key environment variables with the same priority order as model selection:
Component metadata (highest priority)
Environment variable (fallback)

Environment Variables to Add:

OPENAI_API_KEY          # OpenAI components
ANTHROPIC_API_KEY       # Anthropic components  
GOOGLEAI_API_KEY        # Google AI components
MISTRAL_API_KEY         # Mistral components
HUGGINGFACE_API_KEY     # HuggingFace components
BEDROCK_API_KEY         # AWS Bedrock (if needed)

Benefits:

• These are standard, well-known environment variable names already used in the industry.
• Matches existing model selection behavior and develop familiarity when working with model clients
• Runtime flexibility without modifying component metadata

Dapr CLI Integration:
The Dapr CLI should recognize and pass these environment variables to the sidecar when running applications

Related:
Follows the same pattern as the model environment variables implemented in #3792
Addresses the API key configuration gap mentioned in the docs PR discussion