Add support for custom MCP server URLs (#96)

[pontemonti]

• Initial plan

• Add support for custom MCP server URLs

• Add comprehensive tests for custom MCP server URL support

• Remove unnecessary hasattr check in exception handler

• Simplify custom URL checks by removing redundant strip calls

• Improve exception handling and clarify test comments

• Refactor to consistently store URLs in the url field

• Use 'url' field consistently in both manifest and gateway responses

• Refactor gateway parsing to match manifest logic and improve variable naming

• Fix formatting: remove extra blank line in test

• Rename custom_url to endpoint for better clarity

• Remove fallback logic and use config.url directly in all tool registration services

• Remove redundant null check for server_url in Agent Framework service

• Use 'or' operator for cleaner fallback logic in server_name assignment

• Add clarifying comment for server_name fallback logic

• Fix undefined variable reference in log statement

• Move server_name assignment outside try block to ensure it's always available in exception handler

• Clarify comment for server_name fallback logic

• Add server_name fallback logic in OpenAI MCP tool registration service

• Improve variable naming consistency and add server_name fallback in Semantic Kernel service

• Fix inconsistent server_name usage in Semantic Kernel service

• Add server_name fallback logic in configuration service URL construction

• Run ruff formatter to fix formatting issues

• Update tests/tooling/test_mcp_server_configuration.py

• Update tests/tooling/test_mcp_server_configuration.py

• Update tests/tooling/test_mcp_server_configuration.py

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