Move internal crawler to crawler project

[brainless]

As a user, I would like to easily access a crawler for the web. This would allow me to easily research content from the web and grow the knowledge graph. Right now, the crawler is in the graph engine's codebase and that should be moved out since it is not a part of the graph.

Engineering

The separate crawler project uses spider-rs but we can continue building with the simple HTTP request based crawler till we need spider-rs. Let us migrate the simple crawler from within the pixlieai_rs to the crawler project.