[ENHANCEMENT] Q vector generation: path in reciprocal space

**Is your feature request related to a problem? Please describe.**
As far as I can tell, none of the q vector generators in MDANSE can create vectors along a path. (E.g. (0,0,0) -> (0.5,0,0) -> (0.5,0.5,0) ). Also, while I could use the DispersionLatticeQVectors to generate each of these segments separately, it seems that the HKL indices of the points are not written to the output.

**Describe the solution you'd like**
A q vector generator should be added which creates vectors along an arbitrary path.
The way vectors are written to the output file needs to be changed so that the HKL indices of the vectors are saved.
Plotter has to be extended to plot the results as a function of q. (At the moment it only does |q|).

**Describe alternatives you've considered**
Suggestions welcome.

**Additional context**
N/A

Start by reading the existing q vector generators, especially DispersionLatticeQVectors, and inspect how their output records HKL indices. Then trace the Plotter path that currently uses |q|. Done means an arbitrary reciprocal-space path can be generated, HKL indices are preserved in output, and results can be plotted against q.

Written by the indexing model from the issue text.