Provide `.pkg` installer for macOS

Today, we require that macOS users [install the Azure CLI using `brew`](https://docs.microsoft.com/en-us/cli/azure/install-azure-cli-macos?view=azure-cli-latest#install) or taking their chances and installing via [the catch-all bash script](https://docs.microsoft.com/en-us/cli/azure/install-azure-cli-linux?view=azure-cli-latest).

Forcing folks to use brew feels pretty intrusive. Worse yet, if they only use brew for the azure-cli and have Python previously installed, the brew installed python must override the other version or the azure-cli will fail to load some commands.

In regards to the catch-all script, I think it should be reserved for platforms that are less-mainstream than macOS developers.

We've had some asks for this in the past (#7361), but after diagnosing a few failed installs where the root was folks getting bitten by having a mixed brew/system python environment, it's worth another look.