Add a configuration parameter for insecure S3 connections.

[artemdanielyan]

I have minio installed without using HTTPS. When I try to upload backups to an S3 bucket, I get the following errors:

The configuration have next errors:
2 errors occurred:
Failed to init storage `s3` with error: Failed to check bucket exist in S3 storage 's3'. Error: Get "https://111.111.111.111:9000/backups/?location=": http: server gave HTTP response to HTTPS client                                                                                                                                                                                   
* Failed to set storage `minio` for job `prometheus`: storage not available

Please add an option to choose between a secure and an insecure connection to the S3 backend.

[artemdanielyan]

Nevermind, there's actually the option to choose between secure/insecure connections. I couldn't find it in readme at first glance. Added secure: false to my s3 configuration and everything runs as expected