Populate service type for deleted connectors (elastic#181614)

## Summary

This PR updates the connectors usage collector, to populate the
`serviceType` field for deleted connectors.

### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

### For maintainers

- [ ] This was checked for breaking API changes and was [labeled
appropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

Co-authored-by: Kibana Machine <[email protected]>

packages/kbn-search-connectors/lib/collect_connector_stats.ts

@@ -113,6 +113,7 @@ export const collectConnectorStats = async (
     const connectorStats: ConnectorStats = {
       id: connectorId,
       isDeleted: true,
+      serviceType: orphanedSyncJobs[0].connector.service_type,
       syncJobs: syncJobsStats(orphanedSyncJobs),
     };
     connectorStatsArray.push(connectorStats);

packages/kbn-search-connectors/lib/collect_connector_stats_test_data.ts

@@ -249,6 +249,7 @@ export const orphanedSyncJob: ConnectorSyncJob = {
   trigger_method: TriggerMethod.ON_DEMAND,
   connector: {
     id: '3',
+    service_type: 'github',
     configuration: {
       use_text_extraction_service: {
         value: false,
@@ -581,6 +582,7 @@ export const expectedMysqlConnectorStats: ConnectorStats = {
 export const expectedDeletedConnectorStats: ConnectorStats = {
   id: orphanedSyncJob.connector.id,
   isDeleted: true,
+  serviceType: 'github',
   syncJobs: {
     overall: {
       total: 1,