feat: Environment variable naming consistency

[tippmar-nr]

Description

Unifies all environment variable names used by the .NET agent so that they start with NEW_RELIC_ everywhere.

The variable names that changed are as follows:

Old Name	New Name
CORECLR_NEWRELIC_HOME	CORECLR_NEW_RELIC_HOME
NEWRELIC_FORCE_PROFILING	NEW_RELIC_FORCE_PROFILING
NEWRELIC_HOME	NEW_RELIC_HOME
NEWRELIC_INSTALL_PATH	NEW_RELIC_INSTALL_PATH
NEWRELIC_LICENSEKEY	NEW_RELIC_LICENSE_KEY
NEWRELIC_LOG_DIRECTORY	NEW_RELIC_LOG_DIRECTORY
NEWRELIC_LOG_LEVEL	NEW_RELIC_LOG_LEVEL
NEWRELIC_PROFILER_LOG_DIRECTORY	NEW_RELIC_PROFILER_LOG_DIRECTORY
NEWRELIC_AGENT_VERSION_OVERRIDE	NEW_RELIC_AGENT_VERSION_OVERRIDE

Notice (Future breaking change):

The variables in the Old Name column above are still supported with this change, but may be removed in a future major version release of the .NET agent. Users are encouraged to update their installation to use the new names as soon as possible.

Resolves #718

[chynesNR]

When it's time to merge, remember that Notices have to use the notice: prefix in order for Release Please to pick it up. We don't currently have a section for something like "Future Breaking Changes", though we could certainly add one.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 79.16667% with 10 lines in your changes missing coverage. Please review.

Project coverage is 81.32%. Comparing base (9669641) to head (7fa62f0).

Files with missing lines	Patch %	Lines
...c/Agent/Core/Configuration/DefaultConfiguration.cs	25.00%	0 Missing and 6 partials ⚠️
.../NewRelic/Agent/Core/Config/ConfigurationLoader.cs	50.00%	0 Missing and 2 partials ⚠️
...ewRelic/Agent/Core/SharedInterfaces/Environment.cs	66.66%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2812      +/-   ##
==========================================
+ Coverage   81.22%   81.32%   +0.10%     
==========================================
  Files         460      460              
  Lines       29225    29239      +14     
  Branches     3223     3231       +8     
==========================================
+ Hits        23737    23779      +42     
+ Misses       4701     4668      -33     
- Partials      787      792       +5     

Flag	Coverage Δ
Agent	82.23% <65.51%> (-0.02%)	⬇️
Profiler	73.33% <100.00%> (+1.15%)	⬆️

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

Files with missing lines	Coverage Δ
...t/NewRelic/Agent/Core/AgentInstallConfiguration.cs	65.68% <100.00%> (+1.40%)	⬆️
...wRelic/Agent/Core/Config/BootstrapConfiguration.cs	100.00% <100.00%> (ø)
...lic/Agent/Core/SharedInterfaces/EnvironmentMock.cs	29.41% <100.00%> (-6.31%)	⬇️
...NewRelic/Profiler/Logging/DefaultFileLogLocation.h	94.59% <ø> (ø)
...nt/NewRelic/Profiler/MethodRewriter/ISystemCalls.h	100.00% <100.00%> (+53.44%)	⬆️
.../NewRelic/Agent/Core/Config/ConfigurationLoader.cs	81.53% <50.00%> (-0.42%)	⬇️
...ewRelic/Agent/Core/SharedInterfaces/Environment.cs	31.25% <66.66%> (+8.17%)	⬆️
...c/Agent/Core/Configuration/DefaultConfiguration.cs	89.56% <25.00%> (-0.34%)	⬇️

... and 2 files with indirect coverage changes