initial s3 integration

[Screek893]

Use S3 as a storage for reports.

Any S3 compatible bucket is supported.
I used s3fs module, which is a wrapper for boto3.

S3 credentials are configured with env variables (https://s3fs.readthedocs.io/en/latest/index.html#credentials)
for example:

AWS_ACCESS_KEY_ID: 'xxxxxxx'
AWS_SECRET_ACCESS_KEY: 'yyyyyy'
AWS_DEFAULT_REGION: 'region'
AWS_ENDPOINT_URL: '<endpoint_url if it is not AWS S3>'

Add these variables if you want to use s3 as a storage.

STORAGE_TYPE: 's3' # "local" by default
BUCKET_NAME: 'bucket-name'

I am not a python professional. Fell free to review the code and suggest any changes.