Accept multipart form data in /bake

[d98762625]

Motivation: allow users to send files as part of multipart forms to cyberchef-server.

Features:

• send input as "input" field in form:

curl -F "input=<$(pwd)/test-input.txt" -F "recipe=fromHex"  localhost:3000/bake

• send input as "input" file in form:

curl -F "input=@$(pwd)/test-input.txt" -F "recipe=fromHex"  localhost:3000/bake

• recipe must always be a file in the multipart form

Major themes still to complete:

• [x] Only PoC is proven, "make it work => make it good"
• [x] Handle optional outputType property
• [x] Handle input as file, not field