Doc: Add some odoc generated html files to the rdbg section of the user guide

also, use (back) the odoc make rule now the image has been updated

Because currently, the docker image that  builds the pages via the CI
can not run odoc as it require a more recent dune version. It is because
this image used opam 1

using opam 2 would fix this. will do latter

- do not hard-code the size of the graph in the ml files
- do not print the whole state of big graphs. Indeed, for graphs of
  10000 nodes, if we print the path (which is itself an array of size 10000)
  we obtain 100 000 000 variables, which is too much for the rif file.

(i.e., fold_left instead of map + flatten + @)

Indeed, for graphs of 10000 nodes on the dfs, we need to operate
on list of 100 000 000 variables, which overflow the stack.