Sorting plugins custom menu links by category before name

[michaelmicheal]

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In developing custom menu links through plugins, we found that our dropdown menus weren't sorted alphabetically. Digging into it a bit, I found that the menu_links are sorted by name, so the category order is currently somewhat random. Sorting by category and then name keeps the order within a category sorted alphabetically, and sorts the categories alphabetically. Made this change as a patch to our deployments of 2.2.5 and it works great.
Without change:

With change:

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[michaelmicheal]

@ashb Any thoughts on this?

[o-nikolas]

There was a change merged recently to standardize quoting in Airflow, you may need to rebase this PR and run static checks locally to patch those up.
You can enable pre-commit to easily run static checks on your code (readme).