Implement LLM Content Converter node

[dglazkov]

More than likely part of the Gemini Kit, this node will take any text or stream content and turn it into llm-content object.

For example:

• I point core.fetch to a URL that contains a PDF or returns HTML, or a ZIP file
• I wire stream output port of core.fetch to the stream input port of the LLM Content Converter node
• I wire content output port of LLM Content Converter node to the input port of an output node. This input port has type object and llm-content behavior.

When I run the graph, I see content with parts in the output.

[dglazkov]

We could also use this node as the foundation for our ELT work, and keep all conversion in one place.

[paullewis]

This is so exciting!