Add positron to the PATH on installation

[petetronic]

Positron Version: Positron Version: 2023.09.0 (Universal) build 139

Steps to reproduce the issue:

1. Open a Terminal in Mac OS
2. Type positron
3. It reports that the positron command is not found

What did you expect to happen?

We should add positron to the PATH on installation so users can launch positron from the Terminal

Were there any error messages in the output or Developer Tools console?

zsh: command not found: positron

[kevinushey]

I believe this would require us to change the installer generated on macOS from a drag and drop installer to a package installer, so it may require some effort.

[jmcphers]

For users who want to do this it's also very straightforward to set it up post install:

[chendaniely]

this seems like it's part of how VSCode behaves? we have to tell our master's students to go through the same steps for regular VSCode: https://ubc-mds.github.io/resources_pages/install_ds_stack_mac/#visual-studio-code