fix: get-subscription - various issues described below

* Controller needed @transactional. This did not show in the integration tests cos they already had @transactional wrapper on the @test which was a BAD IDEA
* Database event_types needed to be an array i.e. varchar(128)p[]. Puzzled why this did not show on the integrations tests
* Entity needs @Enumerated to ensure its saved as string. Might change this to database enum to avoid this
* Lack of exception handler meant some logging was not showing. We not have a global handler to log everything and rethrow
* Added the missing api-test which would have exhibited the error

Author: coling01

docs/debugging.md

@@ -0,0 +1,25 @@
+# Debugging
+
+The command below will post to create a subscription and return a clientSubscriptionId which can then be queried with GET
+```
+export PORT=4550
+export HOST="localhost:$PORT"
+curl -XPOST http://$HOST/client-subscriptions \
+    -H "Content-Type: application/json" \
+    -d '{"eventTypes":["PCR","CUSTODIAL_RESULT"],"notificationEndpoint":{"webhookUrl":"https://my-callback-url"}}'
+```
+
+... Creates and returns a subscription with a clientSubscriptionId 
+ie.
+```
+{"clientSubscriptionId":"585fde62-44df-4b3d-ac38-5e1f4d7669e3",
+    "createdAt":"2025-12-19T15:16:38.456506Z",
+    "eventTypes":["CUSTODIAL_RESULT","PCR"],
+    "notificationEndpoint":{"webhookUrl":"https://my-callback-url"},"updatedAt":"2025-12-19T15:16:38.456772Z"}
+```
+
+Query
+```
+export SUBSCRIPTION_ID="585fde62-44df-4b3d-ac38-5e1f4d7669e3"
+curl http://$HOST/client-subscriptions/$SUBSCRIPTION_ID
+```