snapshotter: add flag to specify nydus-overlayfs path

[katexochen]

This allows installation of multiple nydus-overlayfs versions on the same machine.

[codecov]

Codecov Report

Attention: Patch coverage is 21.73913% with 18 lines in your changes missing coverage. Please review.

Project coverage is 22.07%. Comparing base (4f4dbcd) to head (50a833f).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
snapshot/mount_option.go	0.00%	10 Missing ⚠️
snapshot/snapshot.go	0.00%	6 Missing ⚠️
config/config.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #615   +/-   ##
=======================================
  Coverage   22.07%   22.07%           
=======================================
  Files         122      122           
  Lines       10746    10766   +20     
=======================================
+ Hits         2372     2377    +5     
- Misses       8054     8068   +14     
- Partials      320      321    +1     

Files with missing lines	Coverage Δ
internal/flags/flags.go	100.00% <100.00%> (ø)
config/config.go	36.28% <0.00%> (-0.66%)	⬇️
snapshot/snapshot.go	0.00% <0.00%> (ø)
snapshot/mount_option.go	23.43% <0.00%> (-0.82%)	⬇️

[imeoer]

LGTM! Maybe also add the option into misc/snapshotter/config.toml. :)

[katexochen]

LGTM! Maybe also add the option into misc/snapshotter/config.toml. :)

Thanks, done! :)