MLI environment variables updated using new naming convention

[AlyssaCote]

SS_INFRA_BACKBONE has been updated to _SMARTSIM_INFRA_BACKBONE and SS_REQUEST_QUEUE is now _SMARTSIM_REQUEST_QUEUE.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Please upload report for BASE (mli-feature@74d6e78). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...tsim/_core/mli/infrastructure/environmentloader.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             mli-feature     #665   +/-   ##
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  Coverage               ?   81.44%           
==============================================
  Files                  ?       97           
  Lines                  ?     7659           
  Branches               ?        0           
==============================================
  Hits                   ?     6238           
  Misses                 ?     1421           
  Partials               ?        0           

Files with missing lines	Coverage Δ
smartsim/_core/launcher/dragon/dragonBackend.py	35.77% <ø> (ø)
...tsim/_core/mli/infrastructure/environmentloader.py	0.00% <0.00%> (ø)

[mellis13]

LGTM!