feat: add prefills for variable payments

[KenLSM]

Problem

Agencies requires a way to programmatically preset the variable payments field. They don't require a hard-prefill nor a verified prefill (i.e., savvy respondents would be able to change the prefills by updating the URL)

Closes FRM-1514

Solution

Expose PAYMENT_VARIABLE_INPUT_AMOUNT_FIELD_ID as the fieldId for prefills.
Read and populate variable payments field if prefill exists.
Validation of values is not performed until the payer interacts with the field -- similar to how soft-prefill works currently.
There's no toggle required for prefills (no need for field_id)

Breaking Changes

• No - this PR is backwards compatible

Tests

Regression

Ensure that prefill works on non-payment forms

• On a regular form
• Toggle on prefill for a Short Text field
• Append prefilled id + data on the URL
• Ensure that the Short Text field is prefilled

Prefills happy flow

• Add a payment variable to a form
• Append ?payment_variable_input_amount_field_id=<amount_in_cents> to the end of the url
• Observe that the variable input field is prefilled

Prefills happy flow with other prefillable fields

• Add a payment variable to a form
• Toggle on prefill for a Short Text field
• Append prefilled id + data on the URL
• Append &payment_variable_input_amount_field_id=<amount_in_cents> to the end of the url (note that we're trying to have two prefills on the URL. 1 for Short Text, another for Variable Payments`
• Observe that the variable input field is prefilled

Prefills invalid data flow

• Create a new payment variable form
• Append ?payment_variable_input_amount_field_id=THIS_IS_NOT_A_NUMBER to the end of the url
• Observe that the variable input field is not prefilled

[linear]

FRM-1514 Add soft pre-fill to payment amount

Description

Problem

Currently our variable payment amount fields are not-prefillable and hence agencies are not able to send specific payment amount links to individuals. Example: NP library fines.

Solution

Make variable payment field soft-prefillable:

• Add prefill toggle
• Prefill the payment amount when passed in the url
• User can update the amount by updating the link.

[wanlingt]

also, I think we can consider getting the InlineMessage (Highlighted fields below have been pre-filled according to the form link you clicked. You may edit these fields if necessary, except non-editable fields with a lock icon.) to show up for the prefilled payment field too (L150 onwards)

[KenLSM]

also, I think we can consider getting the InlineMessage (Highlighted fields below have been pre-filled according to the form link you clicked. You may edit these fields if necessary, except non-editable fields with a lock icon.) to show up for the prefilled payment field too (L150 onwards)

I feel that this might bring too much attention to the variable prefills. This change is currently meant to be for NP's usecase where they want the respondents to simply pay the stated amount. @amitogp wdyt?

[amitogp]

also, I think we can consider getting the InlineMessage (Highlighted fields below have been pre-filled according to the form link you clicked. You may edit these fields if necessary, except non-editable fields with a lock icon.) to show up for the prefilled payment field too (L150 onwards)

I feel that this might bring too much attention to the variable prefills. This change is currently meant to be for NP's usecase where they want the respondents to simply pay the stated amount. @amitogp wdyt?

Agree with @KenLSM, we should not focus much on the variable nature of prefill field. @KenLSM is there a link I can QA to see the current behavior?

[KenLSM]

Update, QA has been done.

[wanlingt]

lgtm!