Propagate self-service flag on uninstalls through to activity (#29691)

Fixes part of unreleased for #28846.

# 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] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements)
- [x] Added/updated automated tests
- [ ] Manual QA for all new/changed functionality

docs/Contributing/reference/audit-logs.md

@@ -1260,6 +1260,7 @@ This activity contains the following fields:
 - "host_display_name": Display name of the host.
 - "software_title": Name of the software.
 - "script_execution_id": ID of the software uninstall script.
+- "self_service": Whether the uninstallation was initiated by the end user from the My device UI.
 - "status": Status of the software uninstallation.
 
 #### Example
@@ -1270,6 +1271,7 @@ This activity contains the following fields:
   "host_display_name": "Anna's MacBook Pro",
   "software_title": "Falcon.app",
   "script_execution_id": "ece8d99d-4313-446a-9af2-e152cd1bad1e",
+  "self_service": false,
   "status": "uninstalled"
 }
 ```