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.
- Use it to send the Content-MD5 header correctly encoded to S3
Gateway
- Fixes a bug in PutObject (including anonymous PutObject) and
PutObjectPart with S3 Gateway found when testing with Mint.
This PR allows 'minio update' to not only shows update banner
but also allows for in-place upgrades.
Updates are done safely by validating the downloaded
sha256 of the binary.
Fixes#4781
Harshavardhana