fix: return IllegalLocationConstraintException for a mismatched LocationConstraint

A region specific endpoint requires CreateBucket to name that same region
in `LocationConstraint`. The gateway reported a mismatch as
`InvalidLocationConstraint`, which AWS reserves for a constraint that is
not a valid location at all, and accepted a request that omitted the
constraint entirely.

Keep `InvalidLocationConstraint` for the global `us-east-1` endpoint,
which takes no constraint, and return
`IllegalLocationConstraintException` when a region specific endpoint gets
a constraint naming another region, or none.

Fixes #2246

s3err/s3err.go

@@ -984,6 +984,20 @@ func GetCopySourceObjectTooLargeErr(limit int64) APIError {
 	}
 }
 
+// Returns illegal location constraint APIError. An empty constraint stands for
+// a CreateBucket request that carried no LocationConstraint at all.
+func GetIllegalLocationConstraintErr(constraint string) APIError {
+	if constraint == "" {
+		constraint = "unspecified"
+	}
+
+	return APIError{
+		Code:           "IllegalLocationConstraintException",
+		Description:    fmt.Sprintf("The %s location constraint is incompatible for the region specific endpoint this request was sent to.", constraint),
+		HTTPStatusCode: http.StatusBadRequest,
+	}
+}
+
 func GetInvalidRedirectCodeErr(input int) APIError {
 	return APIError{
 		Code:           "InvalidRequest",