feat(export-users-clients): add support for exporting users and clients

[galagaevdc]

• Add support for export users and client.
• Verify using exported data in create command

# Users
./mcpjungle create user -c .mcpjungle/users/alice.json

# MCP Clients
./mcpjungle create mcp-client -c .mcpjungle/clients/my-ai-app.json