Exposed more mem_gb parameters and fixed mem_gb_for_model_segments.

[samuelklee]

Closes #4353.
Closes #4362.

[samuelklee]

@LeeTL1220 I went ahead and exposed more mem_gb parameters, which is convenient when we want to go below 250bp and the pair WDL is used as a subworkflow. Please review carefully!

[LeeTL1220]

@samuelklee Looks good.... workflow inputs exist. Each are wired into the correct tasks.

[samuelklee]

Thanks @LeeTL1220, I also added another commit to make some minor comment tweaks. Will merge after tests pass!

[LeeTL1220]

@samuelklee Still looks good.

[codecov-io]

Codecov Report

Merging #4364 into master will increase coverage by 0.003%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #4364       +/-   ##
===============================================
+ Coverage     79.099%   79.102%   +0.003%     
+ Complexity     16659     16658        -1     
===============================================
  Files           1050      1050               
  Lines          59681     59681               
  Branches        9754      9754               
===============================================
+ Hits           47207     47209        +2     
+ Misses          8688      8685        -3     
- Partials        3786      3787        +1

Impacted Files	Coverage Δ	Complexity Δ
...park/sv/discovery/alignment/AlignmentInterval.java	89.272% <0%> (-0.383%)	73% <0%> (-1%)
...e/hellbender/engine/spark/SparkContextFactory.java	73.973% <0%> (+2.74%)	11% <0%> (ø)	⬇️
...utils/smithwaterman/SmithWatermanIntelAligner.java	90% <0%> (+10%)	3% <0%> (ø)	⬇️