feature/mx-1632 structured file support

[ZehraVictoria]

PR Context

So far mex drop only allows JSON file upload.
This establishes compatibility with most common structured file formats.

---

Added

• support for more structured file formats

[mr-kamran-ali]

Nice work. Few little things to fix.

[rababerladuseladim]

Nice work! I do have a few remarks.

First and foremost: One test fails locally: tests/test_main.py::test_index[firefox]

[rababerladuseladim]

Nice, almost done.

A few remarks:

• could you move the helper functions and variables to a dedicated module, e.g. files_io.py?
• I struggled to understand which conversations where fully addressed. To make this easier, we usually work with conversations as follows:
  • the reviewer closes conversations when she/he deems the issues fully addressed
  • the developer adds a comment with the hash of the commit that includes the fix (this facilitates finding of the fix and spotting which conversations you already replied to)

One major remark:
I tried to upload a csv file and get the following error:

{
  "detail": "Content doesn't match extension: application/vnd.ms-excel != Joplin-Setup-3.0.15.csv"
}

I'm not sure who sets that content type, I assume it's the browser. Certainly not me.

[rababerladuseladim]

And one more: could you document the allowed file types in swagger as well? That makes using the API easier.

[ZehraVictoria]

One major remark: I tried to upload a csv file and get the following error:

{
  "detail": "Content doesn't match extension: application/vnd.ms-excel != Joplin-Setup-3.0.15.csv"
}

I'm not sure who sets that content type, I assume it's the browser. Certainly not me.

It seems csv files edited in MS Excel are recognized as application/vnd.ms-excel MIME-type instead of text/csv.
Fixed in 5c69fc5

And one more: could you document the allowed file types in swagger as well? That makes using the API easier.

Also added 5c69fc5. I didn't find anything useful on how to limit the file types in the file selecter popup though

* could you move the helper functions and variables to a dedicated module, e.g. `files_io.py`?

fixed in 35bffdf

[rababerladuseladim]

Biu-ti-ful! And almost there, just some tiny nitpicking left.

[rababerladuseladim]

oh boi, just one tiny thing left.

requested changes applied