Update search session saved object mappings (#154401)

## Summary

Part of https://github.com/elastic/kibana/pull/153070.

Cleans up the saved object mappings for search session saved objects.
Removes the non-searchable/sortable properties from the `mappings`
property and introduces a `schema` property for validation.

src/core/server/integration_tests/saved_objects/migrations/group2/check_registered_types.test.ts

@@ -126,7 +126,7 @@ describe('checking migration metadata changes on all registered SO types', () =>
         "rules-settings": "9854495c3b54b16a6625fb250c35e5504da72266",
         "sample-data-telemetry": "c38daf1a49ed24f2a4fb091e6e1e833fccf19935",
         "search": "ed3a9b1681b57d69560909d51933fdf17576ea68",
-        "search-session": "58a44d14ec991739166b2ec28d718001ab0f4b28",
+        "search-session": "fae0dfc63274d6a3b90ca583802c48cab8760637",
         "search-telemetry": "1bbaf2db531b97fa04399440fa52d46e86d54dd8",
         "security-rule": "1ff82dfb2298c3caf6888fc3ef15c6bf7a628877",
         "security-solution-signals-migration": "c2db409c1857d330beb3d6fd188fa186f920302c",

src/plugins/data/server/search/saved_objects/search_session.ts

@@ -6,6 +6,7 @@
  * Side Public License, v 1.
  */
 
+import { schema } from '@kbn/config-schema';
 import { SavedObjectsType } from '@kbn/core/server';
 import { SEARCH_SESSION_TYPE } from '../../../common';
 import { searchSessionSavedObjectMigrations } from './search_session_migration';
@@ -15,37 +16,14 @@ export const searchSessionSavedObjectType: SavedObjectsType = {
   namespaceType: 'single',
   hidden: true,
   mappings: {
+    dynamic: false,
     properties: {
       sessionId: {
         type: 'keyword',
       },
-      name: {
-        type: 'keyword',
-      },
       created: {
         type: 'date',
       },
-      expires: {
-        type: 'date',
-      },
-      appId: {
-        type: 'keyword',
-      },
-      locatorId: {
-        type: 'keyword',
-      },
-      initialState: {
-        dynamic: false,
-        properties: {},
-      },
-      restoreState: {
-        dynamic: false,
-        properties: {},
-      },
-      idMapping: {
-        dynamic: false,
-        properties: {},
-      },
       realmType: {
         type: 'keyword',
       },
@@ -55,14 +33,32 @@ export const searchSessionSavedObjectType: SavedObjectsType = {
       username: {
         type: 'keyword',
       },
-      version: {
-        type: 'keyword',
-      },
-      isCanceled: {
-        type: 'boolean',
-      },
     },
   },
+  schemas: {
+    '8.8.0': schema.object({
+      sessionId: schema.string(),
+      name: schema.maybe(schema.string()),
+      created: schema.string(),
+      expires: schema.string(),
+      appId: schema.maybe(schema.string()),
+      locatorId: schema.maybe(schema.string()),
+      initialState: schema.maybe(schema.object({}, { unknowns: 'allow' })),
+      restoreState: schema.maybe(schema.object({}, { unknowns: 'allow' })),
+      idMapping: schema.mapOf(
+        schema.string(),
+        schema.object({
+          id: schema.string(),
+          strategy: schema.string(),
+        })
+      ),
+      realmType: schema.maybe(schema.string()),
+      realmName: schema.maybe(schema.string()),
+      username: schema.maybe(schema.string()),
+      version: schema.string(),
+      isCanceled: schema.maybe(schema.boolean()),
+    }),
+  },
   migrations: searchSessionSavedObjectMigrations,
   excludeOnUpgrade: async () => {
     return {