azure-cli: generate completions for all shells

[maxbrunet]

This switches to generate the completion with register-python-argcomplete directly, similarly to other Python tools like pipx.

The az.completion.sh script is not the actual completion, but runs eval: https://github.com/Azure/azure-cli/blob/azure-cli-2.60.0/src/azure-cli/az.completion.sh#L11

This also adds completion support for zsh and fish.

• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

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[carlocab]

Can you also send a PR to update https://github.com/Azure/azure-cli/blob/dev/scripts/release/homebrew/docker/formula_template.txt? Otherwise upstream automation will just overwrite this on their next PR.

[maxbrunet]

Thank you @carlocab for the heads up, I have opened Azure/azure-cli#30032