Create pytorch objects inference fix

[psfoley]

Credit to @sarthakpati for the base implementation!

Proposed Changes

• Correctly populates header information for inference when only validation CSV is provided to create_pytorch_objects function
• Handles a couple other corner cases where training header information is needed
• Used in conjunction with FeTS Challenge 2022

Checklist

• [ x ] I have read the CONTRIBUTING guide
• [ x ] My PR is based from the current GaNDLF master
• [ x ] Non-breaking change (would not break existing functionality): please provide as many details as possible for any breaking change
• Function/class source code documentation added/updated
• Code has been blacked for style consistency
• If applicable, version information has been updated in GANDLF/version.py
• If adding a git submodule, add to list of exceptions for black styling in pyproject.toml file
• Usage documentation has been updated, if appropriate
• History has been updated, if appropriate
• Tests added or modified to cover the changes; if coverage is reduced, please give explanation
• If customized dependency installation is required (i.e., a separate pip install step is needed for PR to be functional), please ensure it is reflected in all the files that control the CI, namely: python-test.yml, and all docker files [1,2,3,4]

[codecov]

Codecov Report

Merging #422 (c471f64) into master (37886ab) will decrease coverage by 0.00%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #422      +/-   ##
==========================================
- Coverage   92.35%   92.34%   -0.01%     
==========================================
  Files         104      104              
  Lines        6082     6088       +6     
==========================================
+ Hits         5617     5622       +5     
- Misses        465      466       +1     

Flag	Coverage Δ
unittests	92.34% <83.33%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
GANDLF/compute/generic.py	94.11% <81.81%> (-2.44%)	⬇️
GANDLF/compute/forward_pass.py	91.89% <100.00%> (+0.03%)	⬆️

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[sarthakpati]

LGTM!

Not merging directly since some of my code was in the merge structure. Thoughts, @Geeks-Sid?

[sarthakpati]

LGTM!