SmartSim environment variables updated using new naming convention

[AlyssaCote]

This PR updates environment variable names with the new convention.

SMARTSIM_DRAGON_SERVER_PATH_EXP -> _SMARTSIM_DRAGON_SERVER_PATH_EXP
RAI_PATH -> SMARTSIM_RAI_LIB
REDIS_PATH -> SMARTSIM_REDIS_SERVER_EXE
REDIS_CLI_PATH -> SMARTSIM_REDIS_CLI_EXE
REDIS_CONF -> SMARTSIM_REDIS_CONF

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Please upload report for BASE (mli-feature@128598b). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
smartsim/experiment.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             mli-feature     #666   +/-   ##
==============================================
  Coverage               ?   71.34%           
==============================================
  Files                  ?      102           
  Lines                  ?     8525           
  Branches               ?        0           
==============================================
  Hits                   ?     6082           
  Misses                 ?     2443           
  Partials               ?        0           

Files with missing lines	Coverage Δ
smartsim/_core/config/config.py	97.14% <100.00%> (ø)
smartsim/_core/utils/helpers.py	91.54% <100.00%> (ø)
smartsim/database/orchestrator.py	81.76% <ø> (ø)
smartsim/experiment.py	85.77% <0.00%> (ø)

[mellis13]

Do we think that this PR should be labeled as an API break?

[ashao]

Some renaming suggestions, but I'm also ok if we don't do it in this PR.