Evalai: Improve challenge creation pipeline

[deshraj]

Current Scenario

If you directly zip the challenge configuration and upload it on the server, then you see an error saying zip file has more than one .yaml files which is mainly the case due to temporary files added to the zip while zipping.

Deliverables

• [ ] Handle the case where temp files are ignored while unzipping in challenge creation API
• [ ] Show a meaningful error rather than showing zip file has more than one .yaml files

How to reproduce

You can reproduce this error by uploading the following challenge zip file to create a challenge.
challenge.zip

[vkartik97]

Can I work on this issue?

[deshraj]

Sure @vkartik97 :)