Refactor such that metadata and etag are
combined to a single argument `srcInfo`.
This is a precursor change for #5544 making
it easier for us to provide encryption/decryption
functions.
Internally, triton-go, what manta minio is built on, changed it's internal
error handling. This means we no longer need to unwrap specific error types
This doesn't change any manta minio functionality - it just changes how errors are
handled internally and adds a wrapper for a 404 error
Manta has the ability to allow users to authenticate with a
username other than the main account. We want to expose
this functionality to minio manta gateway.
Manta is an Object Storage by [Joyent](https://www.joyent.com/)
This PR adds initial support for Manta. It is intended as non-production
ready so that feedback can be obtained.
