feat: Wire up design settings (button colour)

[DafyddLlyr]

What does this PR do?

• Follows on from feat: Wire up design settings (theme colour & logo) #2660
• Wires up button colour form

[github-actions]

Removed vultr server and associated DNS entries

[ianjon3s]

If we include a contrast checker here is must be able to check whether the selected colour contrasts with white or black.

Currently when selecting a light colour (for example Camden's button colour of #ead95b), the text in the button is correctly selected as black, but the form cannot be saved due to validation.

I think we may be best placed to do without a contrast checker here.

[Mike-Heneghan]

Trying this out on the pizza I noticed that the new form does update the DB but the change isn't seen in the flows.

Is that part of the scope of this or is that work elsewhere / to be done later?

[DafyddLlyr]

@Mike-Heneghan Sorry should have clarified that - this code change in this PR doesn't update the button colour directly, that was updated in this PR - #2658

I've just merged that and rebased this PR though so this should now work end-to-end 😄

[Mike-Heneghan]

Looks great and working as expected for me on the pizza now 🥳