Custom ServiceUrl for S3 compatible services

[leonverschuren]

Added the option to override the service url, this makes it possible to use the S3 filesystem with S3 compatible storage providers like DigitalOcean Spaces.

This is the recommended solution by DigitalOcean: https://www.digitalocean.com/community/questions/how-to-use-digitalocean-spaces-with-the-aws-s3-sdks?answer=44888

[LuisNogal]

I tried this with Vultr object storage and it works fine.

[justinstenning]

For containerised solutions like Zenko you may also need to add support for the ForcePathStyle option, e.g.:

src/FubarDev.FtpServer.FileSystem.S3/S3FileSystemOptions.cs:

        /// <summary>
        /// Use path style URLs for S3 (i.e. when using customer endpoints like Zenko)
        /// e.g. https://s3.example.com/bucket/key instead of https://bucket.s3.example.com/key
        /// </summary>
        public bool? ForcePathStyle { get; set; }

src/FubarDev.FtpServer.FileSystem.S3/S3FileSystem.cs:

    config.ServiceURL = options.ServiceUrl;
    config.ForcePathStyle = options.ForcePathStyle == true,