Table with list of default env vars per OS

[seyidaniels]

Fixes #2753

• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation

[gaborbernat]

These are OS angostic

tox/src/tox/tox_env/api.py

Lines 205 to 223 in a261614

	env = [
	"https_proxy", # HTTP proxy configuration
	"http_proxy", # HTTP proxy configuration
	"no_proxy", # HTTP proxy configuration
	"LANG", # localization
	"LANGUAGE", # localization
	"CURL_CA_BUNDLE", # curl certificates
	"SSL_CERT_FILE", # https certificates
	"CC", # C compiler command
	"CFLAGS", # C compiler flags
	"CCSHARED", # compiler flags used to build a shared library
	"CXX", # C++ compiler command
	"CPPFLAGS", # C++ compiler flags
	"LD_LIBRARY_PATH", # location of libs
	"LDFLAGS", # linker flags
	"HOME", # needed for `os.path.expanduser()` on non-Windows systems
	"FORCE_COLOR", # force color output
	"NO_COLOR", # disable color output
	]

[gaborbernat]

Missing PIP_* and VIRTUALENV_* , plus https://github.com/tox-dev/tox/blob/main/src/tox/tox_env/python/api.py#L133