implement OTA enrollment (#21942)

for #21019

# 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. -->

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/Committing-Changes.md#changes-files)
for more information.
- [x] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements)
- [x] Added/updated tests
- [x] Manual QA for all new/changed functionality

server/mdm/microsoft/microsoft_mdm.go

@@ -5,7 +5,7 @@ import (
 	"encoding/base64"
 
 	"github.com/fleetdm/fleet/v4/server/mdm/internal/commonmdm"
-	"go.mozilla.org/pkcs7"
+	"github.com/smallstep/pkcs7"
 )
 
 const (

server/mdm/microsoft/wstep.go

@@ -21,7 +21,7 @@ import (
 	"github.com/fleetdm/fleet/v4/server/mdm/microsoft/syncml"
 	"github.com/fleetdm/fleet/v4/server/mdm/nanomdm/cryptoutil"
 	"github.com/golang-jwt/jwt/v4"
-	"go.mozilla.org/pkcs7"
+	"github.com/smallstep/pkcs7"
 )
 
 // CertManager is an interface for certificate management tasks associated with Microsoft MDM (e.g.,