anyrun: Added margin config option

[Kirottu]

Description

Added the new

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[khaneliman]

Could you update the test

nmt-test-anyrun> Expected home-files/.config/anyrun/config.ron to be same as /nix/store/gajpixa02jsvs4g434gv401myxx3bjia-config.ron but were different:
nmt-test-anyrun> --- actual
nmt-test-anyrun> +++ expected
nmt-test-anyrun> @@ -3,7 +3,6 @@
nmt-test-anyrun>    y: Fraction(0.020000),
nmt-test-anyrun>    width: Absolute(800),
nmt-test-anyrun>    height: Absolute(0),
nmt-test-anyrun> -  margin: 0,
nmt-test-anyrun>    hide_icons: false,
nmt-test-anyrun>    ignore_exclusive_zones: false,
nmt-test-anyrun>    layer: Overlay,