[Logs onboarding] Align elastic-agent version with stackVersion (#162622)

Closes https://github.com/elastic/kibana/issues/159382.

### Changes
- `kibanaVersion` is passed as a resources to the routes.
- `elastic-agent` version is based on `kibanaVersion`.

#### Before
<img width="1073" alt="image"
src="00e291a2-3f8d-4d1d-9520-c0a29cc9454e">

#### After
<img width="1115" alt="image"
src="dffcf95f-f3a2-46f0-bb78-daebe8597b89">

x-pack/plugins/observability_onboarding/server/plugin.ts

@@ -74,6 +74,7 @@ export class ObservabilityOnboardingPlugin
       repository: getObservabilityOnboardingServerRouteRepository(),
       plugins: resourcePlugins,
       config,
+      kibanaVersion: this.initContext.env.packageInfo.version,
       services: {
         esLegacyConfigService: this.esLegacyConfigService,
       },

x-pack/plugins/observability_onboarding/server/routes/custom_logs/route.ts

@@ -16,8 +16,6 @@ import { getHasLogs } from './get_has_logs';
 import { getObservabilityOnboardingState } from './get_observability_onboarding_state';
 import { saveObservabilityOnboardingState } from './save_observability_onboarding_state';
 
-const ELASTIC_AGENT_VERSION = '8.8.0'; // This should be defined from a source with the latest public release
-
 const logMonitoringPrivilegesRoute = createObservabilityOnboardingServerRoute({
   endpoint: 'GET /internal/observability_onboarding/custom_logs/privileges',
   options: { tags: [] },
@@ -46,7 +44,7 @@ const installShipperSetupRoute = createObservabilityOnboardingServerRoute({
     scriptDownloadUrl: string;
     elasticAgentVersion: string;
   }> {
-    const { core, plugins } = resources;
+    const { core, plugins, kibanaVersion } = resources;
     const coreStart = await core.start();
 
     const kibanaUrl =
@@ -59,7 +57,7 @@ const installShipperSetupRoute = createObservabilityOnboardingServerRoute({
     return {
       apiEndpoint,
       scriptDownloadUrl,
-      elasticAgentVersion: ELASTIC_AGENT_VERSION,
+      elasticAgentVersion: kibanaVersion,
     };
   },
 });

x-pack/plugins/observability_onboarding/server/routes/register_routes.ts

@@ -25,6 +25,7 @@ interface RegisterRoutes {
   logger: Logger;
   plugins: ObservabilityOnboardingRouteHandlerResources['plugins'];
   config: ObservabilityOnboardingConfig;
+  kibanaVersion: string;
   services: {
     esLegacyConfigService: EsLegacyConfigService;
   };
@@ -36,6 +37,7 @@ export function registerRoutes({
   logger,
   plugins,
   config,
+  kibanaVersion,
   services,
 }: RegisterRoutes) {
   const routes = Object.values(repository);
@@ -82,6 +84,7 @@ export function registerRoutes({
               },
             },
             config,
+            kibanaVersion,
             services,
           })) as any;
 

x-pack/plugins/observability_onboarding/server/routes/types.ts

@@ -33,6 +33,7 @@ export interface ObservabilityOnboardingRouteHandlerResources {
     start: () => Promise<CoreStart>;
   };
   config: ObservabilityOnboardingConfig;
+  kibanaVersion: string;
   services: {
     esLegacyConfigService: EsLegacyConfigService;
   };