Enhance containerlab's topology file parsing to fetch remote topologies

[hellt]

Instead of doing this

curl -sL srlinux.dev/clab-srl2 | containerlab deploy -c -t -

it would be cooler to be able to just do

containerlab deploy -c -i -t srlinux.dev/clab-srl2

The new -i flag indicates that the contents of a file should be fetched with HTTP instead of cloning this as a repo. Then the fetched bytes should be passed as stding to existing function.

[hellt]

done in #1704