Add SetField Msg

[MattiaVerticchio]

PR Summary for issue #492

• Added the previously commented SetField message
• Implemented a new Cypress test
• In cases where the form or field is not found, I insert the new value with status = NotVisited and submitAttempted = False.

Notes: I attempted to run the Cypress tests from form-submissions.cy.js on a fresh clone of the repository. However, the test that "logs in in with errors, then re-submits the form successfully" is not working due to an issue with the /login route. The error message I encountered was:

BackendTask.Env.expect was expecting a variable `SESSION_SECRET` but couldn't find a variable with that name.

I'm unsure why this issue is occurring, but the new test I implemented passes as expected.

Let me know if this works or if you'd like further adjustments! 😁