Refactor installer to be a PKG

[ThomasK33]

We are currently experiencing issues with the installation and upgrade of Coder Desktop. Specifically, we are encountering this issue, where some component of macOS becomes confused during an update, resulting in a faulty state for both us and the operating system.

We must refactor our installation method to use a package with a pre-install script. This script should:

• Shut down the network extension
• Shut down the desktop client
• Check for any existing Homebrew installations (multiple installations of the network extension can cause issues on macOS)

Implementing these steps should help prevent any disruptions during upgrades.

[ethanndickson]

More relevant threads on the weird behaviour we've been seeing:
https://developer.apple.com/forums/thread/711713 (from above)
https://developer.apple.com/forums/thread/667597
https://developer.apple.com/forums/thread/742992
https://developer.apple.com/forums/thread/728063?answerId=751243022#751243022

Essentially, on-upgrade, the app becomes unable to communicate with the network extension.
This can lead to a incorrect UI state:

Or consistent errors on functionality that requires communcation between the two, such as:

[ethanndickson]

Issue succeeded by #121