docs: update installing/deploying on macOS pages, old versions and broken links

Submitted by Olivier Crête @ocrete

Link to original bug (#773235)

Description

The macOS documentation needs to be updated, in particular, it refers to old versions of macOS and to PackageMaker which has disappeared from Xcode a while ago. So we should possibly have instructions on how to use it with pkgbuild/productbuild.

https://gitlab.freedesktop.org/gstreamer/gstreamer/-/blob/main/subprojects/gst-docs/markdown/installing/on-mac-osx.md?ref_type=heads https://gitlab.freedesktop.org/gstreamer/gstreamer/-/blob/main/subprojects/gst-docs/markdown/deploying/mac-osx.md?ref_type=heads

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https://gstreamer.freedesktop.org/documentation/installing/on-mac-osx.html?gi-language=python https://gstreamer.freedesktop.org/documentation/deploying/mac-osx.html?gi-language=python