feat!(js/plugins/mcp): renamed mcp plugin package to @genkit-ai/mcp and new MCP client API

[pavelgj]

import { createMcpClient } from '@genkit-ai/mcp';

const myFsClient = createMcpClient({
  name: 'myFileSystemClient', // A unique name for this client instance
  command: 'npx',
  args: ['-y', '@modelcontextprotocol/server-everything', '/Users/yourusername/Documents'],
});

async function runSimpleClient() {
  const response = await ai.generate({
    model: googleAI.model('gemini-2.0-flash'), // Replace with your model
    prompt: 'List files in my Documents folder.',
    tools: await myFsClient.getActiveTools(ai),
  });
  console.log(response.text);
}

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)