Fix S3 cache documentation (Amazon's S3 issues)

For Amazon's S3 the ServerAddress should always be s3.amazonaws.com. Minio S3 client will get bucket metadata and modify the URL to point to the valid region (eg. s3-eu-west-1.amazonaws.com) itself.

We should fix the example on Advanced Configuration page and also add a notice about Amazon's S3 URL issue.

Related user's story can be found here: #1198 (closed).

/cc @ayufan @axil

@tmaczukin Could we test it against AWS S3 server?

@ayufan Look at #1198 (closed). There was a problem where user had ServerAddress = "s3-eu-west-1.amazonaws.com" and Minio was logging error Amazon S3 endpoint should be 's3.amazonaws.com'. After changing ServerAddress the error had disappeared.

There is still one problem in #1198 (closed), but I think that it's unrelated with fix proposal in this issue.

Reassigned to @tmaczukin

mentioned in merge request !143 (merged)

Status changed to closed by commit c0fb2b2c09808961280690468062a54c43179221

mentioned in merge request !170 (merged)

added Documentation and removed ~60197 labels