[KP] instrument platform server-side code with apm agent (elastic#70919)

* instrument platform server-side code with apm agent: setup, start lifecycles and SO migration

* add span type

* span should have name: saved_objects.migration

* remove migration reports

* put migration span back

src/core/server/server.ts

@@ -16,7 +16,7 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-
+import apm from 'elastic-apm-node';
 import { config as pathConfig } from '@kbn/utils';
 import { mapToObject } from '@kbn/std';
 import { ConfigService, Env, RawConfigurationProvider, coreDeprecationProvider } from './config';
@@ -106,6 +106,7 @@ export class Server {
 
   public async setup() {
     this.log.debug('setting up server');
+    const setupTransaction = apm.startTransaction('server_setup', 'kibana_platform');
 
     const environmentSetup = await this.environment.setup();
 
@@ -207,20 +208,25 @@ export class Server {
     this.registerCoreContext(coreSetup);
     this.coreApp.setup(coreSetup);
 
+    setupTransaction?.end();
     return coreSetup;
   }
 
   public async start() {
     this.log.debug('starting server');
+    const startTransaction = apm.startTransaction('server_start', 'kibana_platform');
+
     const auditTrailStart = this.auditTrail.start();
 
     const elasticsearchStart = await this.elasticsearch.start({
       auditTrail: auditTrailStart,
     });
+    const soStartSpan = startTransaction?.startSpan('saved_objects.migration', 'migration');
     const savedObjectsStart = await this.savedObjects.start({
       elasticsearch: elasticsearchStart,
       pluginsInitialized: this.#pluginsInitialized,
     });
+    soStartSpan?.end();
     const capabilitiesStart = this.capabilities.start();
     const uiSettingsStart = await this.uiSettings.start();
     const metricsStart = await this.metrics.start();
@@ -248,6 +254,7 @@ export class Server {
 
     await this.http.start();
 
+    startTransaction?.end();
     return this.coreStart;
   }