fix: Revert environment variable name change in installers and scripts

[tippmar-nr]

This PR reverts changes (introduced in #2812) to environment variable names that are set in our installers (MSI, Nuget, etc.) and in various Linux scripts.

The .NET agent still supports both the "old style" environment variable names (those starting with or containing NEWRELIC_) as well as the "new style" environment variable names (those starting with or containing NEW_RELIC_) as called out in #2812. This change simply reverts our installers, etc. to use the "old" names so that existing public documentation related to installing the .NET agent remains correct.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.33%. Comparing base (d312d30) to head (6a4b231).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2852      +/-   ##
==========================================
+ Coverage   81.31%   81.33%   +0.01%     
==========================================
  Files         460      460              
  Lines       29239    29239              
  Branches     3231     3231              
==========================================
+ Hits        23777    23781       +4     
+ Misses       4669     4666       -3     
+ Partials      793      792       -1     

Flag	Coverage Δ
Agent	82.23% <ø> (+0.01%)	⬆️
Profiler	73.33% <ø> (ø)

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see 1 file with indirect coverage changes

[nr-ahemsath]

This is probably the best thing to do under the circumstances.

[nrcventura]

Do we also need to suppress the warning about using the older environment variable name?

[tippmar-nr]

Do we also need to suppress the warning about using the older environment variable name?

No, I think it's ok to keep it. The old names really are deprecated and we want folks to use the new names; we're just making this change to bridge the gap between our docs and the agent.