add ACME forms

Mostly copied from PVE, but the user needs to set the URL
property so their stores can load the data, whereas in PVE
this was hardcoded.

API selector:
  needs its url to point to the challenge-schema url

Acme Account selector:
  needs its url to point to the acme account index

Acme Plugin selector:
  needs its url to point to the plugin index

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>