This refactors the vault configuration by moving the
vault-related environment variables to `environment.go`
(Other ENV should follow in the future to have a central
place for adding / handling ENV instead of magic constants
and handling across different files)
Further this commit adds master-key SSE-S3 support.
The operator can specify a SSE-S3 master key using
`MINIO_SSE_MASTER_KEY` which will be used as master key
to derive and encrypt per-object keys for SSE-S3
requests.
This commit is also a pre-condition for SSE-S3
auto-encyption support.
Fixes#6329
This commit renames the env variable for vault namespaces
such that it begins with `MINIO_SSE_`. This is the prefix
for all Minio SSE related env. variables (like KMS).
Add support for sse-s3 encryption with vault as KMS.
Also refactoring code to make use of headers and functions defined in
crypto package and clean up duplicated code.
