Add minio uploads provider for on-premise deployments

[gcalmettes]

Is your feature request related to a problem? Please describe.
Currently, the files uploads providers are limited to either local path or GCS for object storage, which might be too limiting if one wants to deploy on an on-premise cluster for example. Minio is a great solution for self-hosted object storage and could be proposed as an option.
If of interest, I will be happy to submit a PR for review.

Describe the solution you'd like
For our internal CTF, I have worked on a branch (master...gcalmettes:rctf:feat/uploads-minio-backend) in which I have developed an implementation of a Minio uploads providers (staying as close as possible to the GCS provider logic and syntax), and that conditionally adds the necessary route to proxy the file when this upload provider is selected (in order to allow for a fully private minio service and not needing to create a dedicated DNS for this service)

Describe alternatives you've considered
N/A

Additional context
I will be happy to create a PR if this is of any interest for the project.
Obviously, if this is of interest, I would add the proper addition to the documentation as well as a conditional addition of the minio service in the docker compose.