Root from devcontainer dir

[erichlf]

The main portion of this PR changes from using a git command to find the root of the devcontainer to a pure lua function that searches for the devcontainer closest to the root directory, i.e. /. The toplevel flag determines if we use the closest or furthest up the direcotry tree result.

• Use lua to find uppermost devctontainer
• Add option to find toplevel or nearest
• Separated the logic for running the devcontainer from the window creation.
• Added the ability to cancel bringing up the devcontainer.
• Updated devcontainer.json and Dockerfile to work more generally.
• Removed some multiply defined behaviors
• Add ability to close window with q or escape
• Added on_detach function to handle setting prev_win, win, and buf to -1 after the window is closed
• Use lua to run commands rather than calling a script