Refactor: Move Redundant Form Backend Config Code to Function

[DiogenesAnalytics]

Problem

The code use to update the form backend configuration data is being duplicated all over the place:

• https://github.com/DiogenesAnalytics/parley/blob/e2848d3ddaffce1110439a316010f69b977822b4/tests/test_website.py#L242-L1130