37: add example script to create or update a form

[lindsay-stevens]

Closes #37

What has been done to verify that this works as intended?

Tested with Central staging server.

Why is this the best possible solution? Were any other approaches considered?

Although it boils down to one or two lines, the script shows users how to apply that as a (hopefully) useful script.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

New example script. Though while doing it I noticed a test bug for which a fix is included.

Do we need any specific form for testing your changes? If so, please attach one.

Any form would work.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

Updated docs to refer to the new script.

Before submitting this PR, please make sure you have:

• included test cases for core behavior and edge cases in tests
• run python -m unittest and verified all tests pass
• run ruff format pyodk tests and ruff check pyodk tests to lint code
• verified that any code or assets from external sources are properly credited in comments