New Command Idea: Env

[josephwhite]

Since default environment variables for Zoxide vary across platforms and require some type of processing in Rust, it would be beneficial to add a command to reflect what the environment variables look like after processing.

An new command to stdout the functions in config.rs could also provide a different angle when debugging config issues.

~ > zoxide env --help

Display environment variable solves.

Usage:
   zoxide env <VAR>

Arguments:
   <VAR>  [possible values: _ZO_DATA_DIR, _ZO_ECHO, _ZO_EXCLUDE_DIRS, _ZO_FZF_OPTS, _ZO_MAXAGE, _ZO_RESOLVE_SYMLINKS]