fix(EMS-3385): no PDF - policy - nullify data when changing policy type

[ttbarnes]

Introduction ✏️

This PR fixes an issue where, when changing the policy type from "single" to "multiple" (or vice versa), certain "single" or "multiple" specific policy data would not be wiped.

Resolution ✔️

• Create new cypress commands:
  • changePolicyTypeToSingleAndSubmitContractPolicyForm
  • assertCurrencyFormFieldsAreEmpty
  • assertEmptyContractCompletionDateFieldValues
  • assertEmptyRequestedStartDateFieldValues
• Add an E2E test for changing the policy type from "multiple" to "single", then back to "multiple".
• Add an E2E test for changing the policy type from "single" to "multiple" then back to "single".
• Update mapAndSave.policy to pass application to mapSubmittedData.
• Split up policy data saving mapping functions into their own files/functions:
  • mapDateFields
  • nullifyGenericContractPolicyFields
  • nullifyMultipleContractPolicyFields
  • nullifySingleContractPolicyFields
• Update saveData.policy to not strip empty form fields.
• Create new helper function to determine if a policy type has changed, hasPolicyTypeChanged.

Miscellaneous ➕

• Fix some linting issues.
• Minor documentation improvements.