feat: Add Anthropic Messages API support

[Copilot]

• Analyze existing codebase structure for API endpoints
• Understand OpenAI chat completions implementation pattern
• Research Anthropic API format (Messages endpoint)
• Create Anthropic schema types (request/response)
• Create Anthropic endpoints (messages endpoint)
• Create Anthropic routes registration
• Register Anthropic routes in app.go
• Add unit tests for Anthropic schema
• Fix code review comments (error handling for JSON operations)
• Fix test suite to use existing schema test runner
• Add e2e tests using anthropic-sdk-go for streaming and non-streaming responses
• Run code review
• Run CodeQL security check (no alerts found)

Original prompt

Try to implement #1808. Currently LocalAI does support the openai endpoints. We want to support anthropic ones as well so LocalAI can be used as a drop-in replacement for Anthropic. Specifically we want to support for now only the equivalent of chat completions that we support for OpenAI

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[mudler]

@copilot add an e2e test using https://github.com/anthropics/anthropic-sdk-go as client library for both streaming and non-streaming responses

[Copilot]

@copilot add an e2e test using https://github.com/anthropics/anthropic-sdk-go as client library for both streaming and non-streaming responses

Added e2e tests using anthropic-sdk-go in tests/e2e/e2e_anthropic_test.go covering both non-streaming and streaming responses. The tests verify:

• Non-streaming: message generation, system prompts, and usage information
• Streaming: token streaming with content block delta events and system prompts

Commit: d8a7f43

[mudler]

@copilot create a follow-up PR to also add the tool support to the anthropic endpoints like we do with openai