Add separate udev rules for systemd installs, rework service

On systemd-based systemd, running bootmac directly from the udev rules doesn't work very well. As previously noted, using a systemd service instead fixes those problems, although it requires finding an appropriate "reverse dependency" (such as e.g. bluetooth.target).

Using unit activation from udev makes it easier, at it will be triggered once the interface exists. Moreover, in order to avoid creating multiple service files, we can make it a template and use the instance parameter as bootmac's main command-line argument.

added 2 commits

• 9ab9ff59 - Add separate udev rules for systemd installs, rework service
• 6c6d8451 - Add meson.build

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added status::mr-stale label

Sorry to bother you @a-wai,

but we've detected that this merge request hasn't seen any recent activity. If you need help, want to discuss your approach with developers, or you are all done and this is waiting for review, you can ping @postmarketOS. You can also ask on matrix in #devel:postmarketos.org or #postmarketos-devel on OFTC.

Thanks for your contribution.

@craftyguy can I please ask for your review?