Adding support for MS-MDE2 version 6.0 (#15701)

# Checklist for submitter

If some of the following don't apply, delete the relevant line.

<!-- Note that API documentation changes are now addressed by the
product design team. -->

- [ ] Changes file added for user-visible changes in `changes/` or
`orbit/changes/`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- [ ] Manual QA for all new/changed functionality

server/fleet/microsoft_mdm.go

@@ -147,9 +147,16 @@ func (req *SoapRequest) IsValidDiscoveryMsg() error {
 		return errors.New("invalid discover message: XMLNS")
 	}
 
-	// Ensure that only valid versions are supported
-	if req.Body.Discover.Request.RequestVersion != syncml.EnrollmentVersionV4 &&
-		req.Body.Discover.Request.RequestVersion != syncml.EnrollmentVersionV5 {
+	// Check if the request version is one of the defined enrollment versions
+	versionFound := false
+	for _, v := range syncml.SupportedEnrollmentVersions {
+		if req.Body.Discover.Request.RequestVersion == v {
+			versionFound = true
+			break
+		}
+	}
+
+	if !versionFound {
 		return errors.New("invalid discover message: Request.RequestVersion")
 	}
 

server/mdm/microsoft/syncml/syncml.go

@@ -173,14 +173,14 @@ const (
 	FleetOSUpdateTargetLocURI  = "/Vendor/MSFT/Policy/Config/Update"
 )
 
+// Supported MS-MDE2 enrollment versions
+var SupportedEnrollmentVersions = []string{"4.0", "5.0", "6.0"}
+
 // MS-MDE2 Message constants
 const (
-	// Minimum supported version
+	// Default MS-MDE2 enrollment protocol version
 	EnrollmentVersionV4 = "4.0"
 
-	// Maximum supported version
-	EnrollmentVersionV5 = "5.0"
-
 	// xsi:nil indicates value is not present
 	DefaultStateXSI = "true"