Badge mixin

[russbiggs]

Although we dont have a direct need for it. It may be nice to create a mixin for the badges so that custom colors etc can be defined outside of the 3 colors explicitly defined in the current design file. e.g.

@use 'openaq-design-system/variables' as variables;
@use 'openaq-design-system/mixins' as mixins;

@include mixins.badge(variables.$oceans)