Make optical primary generator distributions configurable

[amandalund]

Previously our optical primary generator was hardcoded to sample a point source of mono-energetic isotropic photons. This updates the generator and data to support runtime-configurable distribution types from user input. I've also added an input option for a Gaussian energy distribution.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 94.30052% with 11 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 84.93%. Comparing base (57aed2a) to head (5c6cd56). :warning: Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...corecel/random/distribution/DistributionVisitor.hh	81.25%	6 Missing :warning:
src/celeritas/phys/PrimaryGenerator.cc	89.28%	3 Missing :warning:
src/celeritas/phys/PrimaryGeneratorOptions.cc	60.00%	2 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2122      +/-   ##
===========================================
+ Coverage    84.90%   84.93%   +0.03%     
===========================================
  Files         1254     1259       +5     
  Lines        44128    44273     +145     
  Branches     16645    16372     -273     
===========================================
+ Hits         37465    37602     +137     
+ Misses        4873     4860      -13     
- Partials      1790     1811      +21     

Files with missing lines	Coverage Δ
src/celeritas/inp/Events.hh	69.23% <100.00%> (-4.11%)	:arrow_down:
src/celeritas/optical/gen/GeneratorData.hh	82.75% <ø> (+0.40%)	:arrow_up:
src/celeritas/optical/gen/PrimaryGenerator.hh	100.00% <100.00%> (ø)
...rc/celeritas/optical/gen/PrimaryGeneratorAction.cc	85.13% <100.00%> (+0.84%)	:arrow_up:
src/celeritas/optical/gen/PrimaryGeneratorData.hh	100.00% <100.00%> (ø)
...tas/optical/gen/detail/PrimaryGeneratorExecutor.hh	100.00% <100.00%> (ø)
src/celeritas/phys/PrimaryGeneratorOptions.hh	100.00% <ø> (ø)
src/corecel/grid/SplineDerivCalculator.hh	100.00% <ø> (ø)
src/corecel/inp/Distributions.hh	100.00% <100.00%> (ø)
src/corecel/math/ArrayUtils.hh	98.78% <100.00%> (+0.09%)	:arrow_up:
... and 11 more

... and 25 files with indirect coverage changes

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[github-actions[bot]]

Test summary

 5 722 files   9 188 suites   17m 55s :stopwatch:  2 085 tests  2 059 :white_check_mark:  26 :zzz: 0 :x: 31 913 runs  31 765 :white_check_mark: 148 :zzz: 0 :x:

Results for commit 5c6cd561.

:recycle: This comment has been updated with latest results.

[sethrj]

Could you also move https://github.com/celeritas-project/celeritas/pull/2122/commits/953ab1ee9f9500b7c4ccbb8385d8a8b4f5e90079 to a little separate PR? It's a significant enough change.