Add one time donations to membership builder

[aiscarvalho]

We updated the membership builder to reflect the changes in the join flow (revised slides and one time donations):

Design spec on penpot

[wpf500]

Looks good. My only comment is that the sales tax setting is in the join form tab but applies to one-time donations too, which doesn't quite make sense.

Thinking about it, the sales tax should probably be under settings somewhere instead as it is really a system-wide change, it affects the join form, invoices, update contribution form, etc. So I think we can remove it from the membership builder and stick it in settings somewhere

[wpf500]

@aiscarvalho can you remove the sales tax from these designs for completeness, but I don't think there's any need to design something for the settings page. We can just add a quick form to the general tab for now.

[aiscarvalho]

@wpf500 when updating the spec to remove the sales tax setting we noticed that some of the screens on the one time contribution's flow were missing in the admin interface. We added them now:

After adding all the flow screens to the membership builder we noticed a few interface problems that arise in long pages such as the one time contributions: the save button gets hidden at the end, the page title & tabs also get hidden and the user looses a bit of context. To prevent this we added a few informative texts near each screen and we were wondering if its possible to enable auto save (to prevent that updates get lost).

Maybe in the future we could revise the horizontal tabs and the way we show the different flow steps. We though about the slides interface, when editing callouts (admin). Maybe it would make sense to have something similar here, to navigate between the different flow slides.

Thank you!