Fix cluster call responses that are missing source fields (#118642) (#118698)

Change usage from `_source: 'true'` to `_source: true`.

Co-authored-by: Joe Portner <5295965+jportner@users.noreply.github.com>

packages/kbn-es-archiver/src/lib/docs/generate_doc_records_stream.test.ts

@@ -121,7 +121,7 @@ describe('esArchiver: createGenerateDocRecordsStream()', () => {
       "calls": Array [
         Array [
           Object {
-            "_source": "true",
+            "_source": true,
             "index": "bar",
             "query": undefined,
             "rest_total_hits_as_int": true,
@@ -136,7 +136,7 @@ describe('esArchiver: createGenerateDocRecordsStream()', () => {
         ],
         Array [
           Object {
-            "_source": "true",
+            "_source": true,
             "index": "foo",
             "query": undefined,
             "rest_total_hits_as_int": true,

packages/kbn-es-archiver/src/lib/docs/generate_doc_records_stream.ts

@@ -38,7 +38,7 @@ export function createGenerateDocRecordsStream({
             index,
             scroll: SCROLL_TIMEOUT,
             size: SCROLL_SIZE,
-            _source: 'true',
+            _source: true,
             query,
             rest_total_hits_as_int: true,
           },

src/core/server/saved_objects/service/lib/repository.ts

@@ -1825,7 +1825,7 @@ export class SavedObjectsRepository {
       index: this.getIndexForType(type),
       refresh,
       require_alias: true,
-      _source: 'true',
+      _source: true,
       body: {
         script: {
           source: `