Add backup functionality

[gpetretto]

Initial implementation of a backup feature to create and restore a dump of the queue store. Closes #165.
Two options either based on the presence of the mongodump/mongorestore executable in the system, or a simple python dump to BSON files.
This may be important to have once we put in place the automatic update procedure (see #150). It might be convenient to suggest the users to perform a backup before proceeding with the update of the DB.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 19.33333% with 121 lines in your changes missing coverage. Please review.

Project coverage is 47.17%. Comparing base (00b7f22) to head (0d86cae).

Files with missing lines	Patch %	Lines
src/jobflow_remote/utils/db.py	20.58%	53 Missing and 1 partial ⚠️
src/jobflow_remote/jobs/jobcontroller.py	5.66%	50 Missing ⚠️
src/jobflow_remote/cli/backup.py	39.28%	17 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #190      +/-   ##
===========================================
- Coverage    47.99%   47.17%   -0.82%     
===========================================
  Files           43       44       +1     
  Lines         5165     5314     +149     
  Branches      1121     1164      +43     
===========================================
+ Hits          2479     2507      +28     
- Misses        2429     2549     +120     
- Partials       257      258       +1     

Files with missing lines	Coverage Δ
src/jobflow_remote/cli/__init__.py	100.00% <100.00%> (ø)
src/jobflow_remote/cli/backup.py	39.28% <39.28%> (ø)
src/jobflow_remote/jobs/jobcontroller.py	33.91% <5.66%> (-1.69%)	⬇️
src/jobflow_remote/utils/db.py	50.00% <20.58%> (-14.50%)	⬇️

[davidwaroquiers]

Great addition! A few comments/questions/suggestions here and there

[gpetretto]

I addressed the comments above. I still need to prepare the documentation of the feature

[davidwaroquiers]

All good to me! Great doc.