Fix MDM last checkin and enrollment names to match API spec (#29073)

For #17710 

I focused too much on making sure we were returning the requested data
and got the actual property names wrong.

See https://github.com/fleetdm/fleet/pull/28940/files for proper names

- [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 automated tests
- [x] Manual QA for all new/changed functionality

cmd/fleetctl/fleetctl/testdata/expectedHostDetailResponseJson.json

@@ -53,8 +53,8 @@
       "server_url": null,
       "connected_to_fleet": null
     },
-    "mdm_last_seen_at": null,
-    "mdm_last_enrolled_at": null,
+    "last_mdm_checked_in_at": null,
+    "last_mdm_enrolled_at": null,
     "team_id": null,
     "pack_stats": null,
     "team_name": null,

cmd/fleetctl/fleetctl/testdata/expectedHostDetailResponseYaml.yml

@@ -30,6 +30,8 @@ spec:
   label_updated_at: "0001-01-01T00:00:00Z"
   labels: []
   last_enrolled_at: "0001-01-01T00:00:00Z"
+  last_mdm_checked_in_at: null
+  last_mdm_enrolled_at: null
   last_restarted_at: "0001-01-01T00:00:00Z"
   logger_tls_period: 0
   mdm:
@@ -41,8 +43,6 @@ spec:
     pending_action: ""
     server_url: null
     connected_to_fleet: null
-  mdm_last_enrolled_at: null
-  mdm_last_seen_at: null
   memory: 0
   orbit_version: null
   os_version: ""