Move environment functionality to utils

[mjcarroll]

Since multiple ignition libraries make use of setting/getting environment variables, it makes more sense to locate it here.

[codecov-commenter]

Codecov Report

Merging #30 (ac3a46e) into ign-utils1 (bb3f23a) will increase coverage by 0.36%.
The diff coverage is 95.23%.

@@              Coverage Diff               @@
##           ign-utils1      #30      +/-   ##
==============================================
+ Coverage       94.00%   94.36%   +0.36%     
==============================================
  Files               3        4       +1     
  Lines              50       71      +21     
==============================================
+ Hits               47       67      +20     
- Misses              3        4       +1     

Impacted Files	Coverage Δ
src/Environment.cc	95.23% <95.23%> (ø)

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[chapulina]

LGTM with green CI

[azeey]

LGTM. The only caveat is that I don't think env and setenv are thread safe since the underlying functions are not. I'm not referring to the issue of a global char * getting invalidated by multiple calls to getenv from different threads, but the data race that can occur when both setenv and getenv are called from different threads. The windows documentation recommends synchronizing calls to these functions. cppreference for getenv says:

This function is thread-safe (calling it from multiple threads does not introduce a data race) as long as no other function modifies the host environment. In particular, the POSIX functions setenv(), unsetenv(), and putenv() would introduce a data race if called without synchronization.

Perhaps we can just document this in Environment.hh.

[mjcarroll]

Perhaps we can just document this in Environment.hh.

Added documentation.

[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-03-01-citadel-edifice-fortress/1313/1