[APM] Fix: Add tracing sample missing fields in the overview (elastic…

…#206932)

Closes elastic#200474

## Summary

This PR fixes the issue with tracing sample missing URL/Status Code/User
Agent fields in the overview

## Testing
- Open the APM UI and find APM traces that contains `url.full` /
`transaction.page.url`, `http.request.method` and
`http.response.status_code`
- One should be ingested using an otel collector the other should use an
apm-server
- if using oblt cluster you can check transactions from `loadgenerator`
and `opbeans-python` for example
    - check the trace summary:
        - Otel:

![image](https://github.com/user-attachments/assets/871172b6-8307-4aa2-844e-73a8405da746)

        - APM server:

![image](https://github.com/user-attachments/assets/ef233cf4-0fbb-49c2-8f09-d4299a34ec8c)

(cherry picked from commit 1d493c0)

x-pack/solutions/observability/packages/kbn-apm-types/src/es_schemas/raw/fields/user_agent.ts

@@ -10,7 +10,7 @@ export interface UserAgent {
     name: string;
   };
   name?: string;
-  original: string;
+  original?: string;
   os?: {
     name: string;
     version?: string;

x-pack/solutions/observability/plugins/apm/server/routes/transactions/get_transaction/index.ts

@@ -25,6 +25,11 @@ import {
   SPAN_LINKS,
   TRANSACTION_AGENT_MARKS,
   SERVICE_LANGUAGE_NAME,
+  URL_FULL,
+  HTTP_REQUEST_METHOD,
+  HTTP_RESPONSE_STATUS_CODE,
+  TRANSACTION_PAGE_URL,
+  USER_AGENT_NAME,
 } from '../../../../common/es_fields/apm';
 import { asMutableArray } from '../../../../common/utils/as_mutable_array';
 import type { APMEventClient } from '../../../lib/helpers/create_es_client/create_apm_event_client';
@@ -58,7 +63,15 @@ export async function getTransaction({
     TRANSACTION_TYPE,
   ] as const);
 
-  const optionalFields = asMutableArray([PROCESSOR_NAME, SERVICE_LANGUAGE_NAME] as const);
+  const optionalFields = asMutableArray([
+    PROCESSOR_NAME,
+    SERVICE_LANGUAGE_NAME,
+    URL_FULL,
+    TRANSACTION_PAGE_URL,
+    HTTP_RESPONSE_STATUS_CODE,
+    HTTP_REQUEST_METHOD,
+    USER_AGENT_NAME,
+  ] as const);
 
   const resp = await apmEventClient.search('get_transaction', {
     apm: {