[BUG] Completions can't install on Apple Silicon Macs (or when `/usr/local/share/zsh/` doesn't exist)

[willdhorn]

Describe the bug
CLI completions fail to install when /usr/local/share/zsh/ doesn't exist, which it won't on Apple Silicon macs because /usr is protected.

To Reproduce

1. make sure /usr/local/share/zsh/ doesn't exist
2. run doppler completion install
3. See error

Expected behavior
Either:

• it adds the file(s) to a different directory and adds it to $FPATH
• the cli supports a flag to specify a directory to place the completions and adds that directory to $FPATH

Desktop (please complete the following information):
macOS Ventura 13.6.1 (M2 MacBook Pro)

CLI Version:
v3.68.0

Additional Context
/usr requires root permissions on Apple Silicon Macs. This is why homebrew completions are installed in /usr/local/share/zsh/site-functions on x86 macs and /opt/homebrew/share/zsh/site-functions on ARM machines.

[nmanoogian]

Thanks for reporting this @willdhorn! We'll take a look.