Enable editing of files in a running container

[philliphoff]

An earlier feature added viewing (read-only) of files in a running container. This issue builds on top of that functionality to enable editing (and saving) of those files back to the container.

[dbreshears]

make sure we can track the usage

[aviadcye]

Any news on this?

[philliphoff]

@aviadcye It's being worked on. :-) See #2671.