feat: Fix HASTUS exports with existing service IDs

[jzimbel-mbta]

Summary of changes

Asana Ticket: 🏹 Handle duplicate service IDs in HASTUS imports

Summary of approach

During parsing of the uploaded HASTUS export zip:

• Check if any service IDs in the export already exist in hastus_services table.
• If they do, immediately amend the export so that the IDs are unique, and indicate to the LiveView that the export was amended.
  This ensures that we don't keep any bad export data in memory that could accidentally be saved to the DB or uploaded to S3.

If the export was amended during parsing:

• Replace the save / cancel buttons with a warning about the duplicate service IDs, and ask user for confirmation
• If user clicks Yes, clear the warning and show the usual save / cancel buttons. (The export has already been amended, so no additional processing is needed.)
• If user clicks No, cancel the entire upload.

Reviewer Checklist

• Meets ticket's acceptance criteria
• Any new or changed functions have typespecs
• Tests were added for any new functionality (don't just rely on Codecov)
• This branch was deployed to the staging environment and is currently running with no unexpected increase in warnings, and no errors or crashes.

[lemald]

@jzimbel-mbta I'm going to wait on seeing the final version and the tests before actually approving, but I've taken a look over what you've got so far and I think it looks mostly good - no comments for the moment. 👍