ls(1): Enable colors with COLORTERM is set in the environment

COLORTERM is the de facto standard, while CLICOLOR is generally specific to
FreeBSD and ls(1).

PR: 230101
Submitted by: D Green <dfrg@xsmail.com> (with manpage additions by myself)
Reviewed by: cem ("LGTM" in PR; pre-manpage changes)
MFC after: 1 week