Update document capture to use request utility

[aduth]

🛠 Summary of changes

Updates fetch usage in document capture to use the @18f/identity-request utility.

Why?

• For consistent handling of CSRF token
  • Simplifies behavior within document capture to remove concern for csrf React context value
  • Ensures that document capture keepalive behavior works the same way to refresh the global CSRF token as introduced with Add automatic CSRF refresh on session keepalive #8067
• Expands features of @18f/identity-request to support use-case of raw response handling

📜 Testing Plan

• Ensure no regressions in document capture submission

[aduth]

There's some failing tests I'll need to work through. Reverting to draft for now.

[aduth]

Tests should hopefully be fixed now. Just needed to sync them to (1) new expectation that CSRF is not an implementation detail of the document capture's upload and (2) use real Response values in fetch stubbing, since the request utility expects to be able to read from the response headers.