Feat/pdjb 634 gas upload page

[AEPR]

Ticket number

PDJB-634

Goal of change

Add the file upload page to the registration journey.

Description of main change(s)

Implements the gas upload page as part of the property registration journey.

Extra changes/improvements:

• Deletes virus scan callbacks when they are processed
• Switch to using a sealed class for virus callbacks

Anything you'd like to highlight to the reviewer?

Include e.g. anything unusual about the PR, where there was some debate over how to implement it, or anywhere you were
unsure of the approach to take and would like specific feedback.

Checklist

Delete any that are not applicable, and add explanation below for any that are applicable but haven't been done

• Screenshots of any UI changes have been added
• Unit tests for new logic (e.g. new service methods) have been added
• Single page integration tests have been added for any unhappy-flow UI features, e.g. validation errors
• New journey steps have been added to the appropriate journey integration test(s)
• Test suite has been run in full locally and is passing
• Branch has been rebased onto main and run locally, with everything working as expected (both for your new feature
  and any related functionality)
• TODO comments referencing this JIRA ticket have been searched for and removed - if a future PR will address them,
  mention that here
• Seed data has been updated as needed for your feature to be tested without having to e.g. register a new property
• NftDataSeeder has been updated to reflect any changes to the database schema
• QA instructions have been added to the ticket (particularly if this is the last PR required to complete the ticket)

[Travis-Softwire]

A few minor points, but LGTM