Add support for SSE-S3 server side encryption with vault (#6192)

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.

vendor/github.com/hashicorp/hcl/lex.go

@@ -0,0 +1,38 @@
+package hcl
+
+import (
+	"unicode"
+	"unicode/utf8"
+)
+
+type lexModeValue byte
+
+const (
+	lexModeUnknown lexModeValue = iota
+	lexModeHcl
+	lexModeJson
+)
+
+// lexMode returns whether we're going to be parsing in JSON
+// mode or HCL mode.
+func lexMode(v []byte) lexModeValue {
+	var (
+		r      rune
+		w      int
+		offset int
+	)
+
+	for {
+		r, w = utf8.DecodeRune(v[offset:])
+		offset += w
+		if unicode.IsSpace(r) {
+			continue
+		}
+		if r == '{' {
+			return lexModeJson
+		}
+		break
+	}
+
+	return lexModeHcl
+}