Migrate Jira and Salesforce examples from plugins to Python endpoints

[bgaidioz]

Refactors both the Jira and Salesforce examples to use direct Python MCP endpoints instead of the plugin-based approach. This makes both integrations much simpler and more maintainable.

Key changes:

• Replaced plugins with direct Python functions in jira_endpoints.py and salesforce_endpoints.py
• Updated all tool definitions to call Python functions instead of SQL UDFs
• Changed configuration to use secrets instead of plugin config
• Added comprehensive tests for all endpoints
• Removed SQL wrapper files that are no longer needed

Benefits:

• No custom plugins required - just plain Python functions
• Direct MCP tool calls without SQL wrapper layer
• Simpler configuration and easier debugging
• More flexible return types (JSON instead of SQL strings)
• Demonstrates the Python endpoint pattern for future integrations