feat: write the docs about the AnyFlow MCP

[yudikubota]

This PR:

• Remove keytar docs;
• Make a section about AnyFlow MCP, its features, and examples;
• Implements a plugin to serve and build the llms.txt file dinamically;
• Fix FAQ;
• Upgrades Docusaurus version;
• Adds a llms.txt link to the bottom of the sidebar.

Note:

• There are sections on the docs left with TODO (support coming soon). They will be addressed on the future updates.