feat: custom endpoint for amazon s3
As many object-storage service providers other than Amazon provide S3-compatible APIs, being able to configure custom endpoints different from s3.amazonaws.com allows several third-party providers (e.g. Tencent Cloud, Alibaba Cloud) to be used. For example, after setting endpoint to cos.ap-guangzhou.myqcloud.com, Tencent Cloud object storage can act as a drop-in replacement for Amazon S3.
This commit adds a new key in AWSOptions called endpoint. If specified, it will be used for all AWS S3 SDK calls, as well as calculating the path used for frontend preview.
Also, PR#34 might be covered by this, since minio is compatible with S3.
@dziraf any chance to this MR be merged?