fixes 433: convert latin1 to utf for filenames return by multer

[sadiqkhoja]

Closes getodk/central#433

Root cause:

Multer is parsing filename with latin1 encoding instead of UTF-8. expressjs/multer#1104

What has been done to verify that this works as intended?

• Tested locally + integration test

Why is this the best possible solution? Were any other approaches considered?

Created local middleware to convert latin1 encoding to utf8

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

This is localized changed, if submission are tested from Enketo and Collect are tested then we should be good

Does this change require updates to the API documentation? If so, please update docs/api.md as part of this PR.

None

Before submitting this PR, please make sure you have:

• run make test-full and confirmed all checks still pass OR confirm CircleCI build passes
• verified that any code from external sources are properly credited in comments or that everything is internally sourced

[lognaturel]

Thank you @sadiqkhoja

Not great that a seemingly routine dependency version bump led to data loss because of a subdependency change. A good reminder that we are at the mercy of our dependencies. Not sure there's anything we could have done differently to catch this one.