Long form --mount to support special chars in bind mount paths etc.

[dtrudg]

Is your feature request related to a problem? Please describe.
A path containing a : cannot be bind mounted.

Describe the solution you'd like
One approach is an escaping pattern as in apptainer/singularity#6008 - but the changes introduce further deep nested logic in the bind mount parsing.

It may be useful to consider how docker does this with a verbose --mount flag that uses type=,source=,destination= to avoid escaping problems.

moby/moby#8604

See commentary on the hpcng issue: apptainer/singularity#5923

[dtrudg]

Convinced now that using a long form --mount syntax is the way to go here. We will gain some basic compatibility with Docker, for tools/manual use where it's advantageous to have common syntax for bind mounts when calling docker and Singularity.

We can also in future look at supporting the propagation and recursion options Docker exposes, and allowing type=tmpfs mounts as Docker does, if these would be useful to people.

Please let me know here if you think I'm misguided :-)