Add Azure OpenAI provider with configuration options and tests

[TheRealNeil]

This pull request adds first-class support for Azure OpenAI as a provider in the codebase, including configuration, authentication, and endpoint handling. It introduces a dedicated provider class for Azure OpenAI, options for Azure-specific configuration, and ensures compatibility with various naming conventions. The changes also include new VCR test fixtures to verify integration with Azure OpenAI endpoints.

Azure OpenAI Provider Implementation:

• Added AzureProvider class in lib/active_agent/providers/azure_provider.rb, which extends the OpenAI provider to support Azure-specific authentication (using the api-key header), endpoint structure, and required query parameters like api-version. Also introduces an AzureClient subclass to handle these specifics.
• Added Azure-specific options class in lib/active_agent/providers/azure/options.rb, supporting configuration of azure_resource, deployment_id, and api_version, with validation and sensible defaults.
• Added type and dependency requirements for Azure provider in lib/active_agent/providers/azure/_types.rb.

Provider Aliasing and Naming Consistency:

• Updated the provider service name remapping in lib/active_agent/concerns/provider.rb to recognize multiple Azure OpenAI naming variants (e.g., AzureOpenai, Azureopenai → AzureOpenAI).
• Added alias files (azure_open_ai_provider.rb, azure_openai_provider.rb, azureopenai_provider.rb) to ensure all common naming conventions load the Azure provider. [1] [2] [3]

Testing and Integration:

• Added new VCR cassette fixtures for various Azure OpenAI chat completion scenarios (single instruction, multiple instructions, developer message, system with user), verifying correct API interactions and responses. [1] [2] [3] [4]