adding random removal in haddock3-restraint cli

[VGPReys]

Checklist

• Tests added for the new code
• Documentation added for the code changes
• Does not break licensing
• Does not add any dependencies, if it does please add a thorough explanation

Summary of the Pull Request

This pull request adds the random_removal sub-command to the haddock3-restraints CLI.

Given an input ambiguous file (.tbl), this subcommand will generate an archive containing multiple tbl files, each containing a subset of the initial ones.

The subset is tuned by the optional argument --ratio (-r), defining the ratio of restraints to be removed (between 0 and 1), 0 not doing anything and 1 removing everything...
The number of generated files in the archive is tuned by the argument --nb-tbl (-n)
The random seed can be tuned using --seed (-s), for reproducibility issues

Usage:
haddock3-restraints random_removal <tbl_file> [-r <ratio>] [-n <nb-tbl>] [-s <seed>]

options:
  -h, --help            show this help message and exit
  -r RATIO, --ratio RATIO
                        Ratio of restraints to be randomly removed.
  -s SEED, --seed SEED  Pseudo-random seed.
  -n NB_TBL, --nb-tbl NB_TBL
                        Number of ambiguous files to generate in the archive.

Related Issue

Closes #1240

Additional Info

The functions managing the random removal are placed in librestraints.py, allowing for their usage outside of this CLI.
For example, directly in the CNS modules, such as rigidbody, flexref, etc...

[rvhonorato]

There is no issue associated with this PR - please add one before merging