[Feature] Fix issues that cause Veteran Evidence Doc Upload silent failures

[lisacapaccioli]

Reducing future silent upload failures for Veteran evidence uploads.

The purpose of this work is to fix the actual causes for the silent uploads. This may require frontend and/or backend work, of which we won't know what that is until the discovery feature has been conducted.

The issue is, a veteran uploads something. Sometimes, a lot of times, we accept it, allow the veteran to submit, their entire 526 application (including the evidence they uploaded) and then, due to either mismatched, or missing, or whatever, requirement enforcement, go to upload their file that we have already accepted, and it fails, but they already submitted and are gone, thinking they are all good.

We want to use the validate endpoint to check the validity of the uploaded files, themselves, as the user uploads, so that we can eliminate that possibility from happening, without having to re-impliment (and maintain when/if they change) the lighthouse endpoint upload requirements

Goals

• The fixes work should solve for these:
• Prevent future silent Veteran evidence failures
  • alerting users early that their document could not be succesfully upload
  • fixing the problems where the system failed to upload properly
• Confirming that the current validations align with the external services' requirements (e.g., EVSS, LH, etc)

Dependencies

• [Discovery Feature] Veteran Evidence Document Upload Historical Silent Failures
  #88534
• [Epic] Lighthouse Document Upload Migration
  #83837