[Enterprise Search]Add Document Level Security feature flag (#158538)

## Summary

Adds a featureFlag from config to enable/disable Document Level Security
elements.

Flag is `hasDLSEnabled`, and available through Kea, Kibana Logic.

### Checklist


- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

x-pack/plugins/enterprise_search/common/__mocks__/initial_app_data.ts

@@ -34,6 +34,7 @@ export const DEFAULT_INITIAL_APP_DATA = {
   features: {
     hasConnectors: true,
     hasDefaultIngestPipeline: true,
+    hasDocumentLevelSecurityEnabled: true,
     hasNativeConnectors: true,
     hasWebCrawler: true,
   },

x-pack/plugins/enterprise_search/common/constants.ts

@@ -172,6 +172,7 @@ export enum INGESTION_METHOD_IDS {
 export const DEFAULT_PRODUCT_FEATURES: ProductFeatures = {
   hasConnectors: true,
   hasDefaultIngestPipeline: true,
+  hasDocumentLevelSecurityEnabled: true,
   hasNativeConnectors: true,
   hasWebCrawler: true,
 };

x-pack/plugins/enterprise_search/common/types/index.ts

@@ -39,6 +39,7 @@ export interface ProductAccess {
 export interface ProductFeatures {
   hasConnectors: boolean;
   hasDefaultIngestPipeline: boolean;
+  hasDocumentLevelSecurityEnabled: boolean;
   hasNativeConnectors: boolean;
   hasWebCrawler: boolean;
 }

x-pack/plugins/enterprise_search/server/index.ts

@@ -22,6 +22,7 @@ export const configSchema = schema.object({
   enabled: schema.boolean({ defaultValue: true }),
   hasConnectors: schema.boolean({ defaultValue: true }),
   hasDefaultIngestPipeline: schema.boolean({ defaultValue: true }),
+  hasDocumentLevelSecurityEnabled: schema.boolean({ defaultValue: true }),
   hasNativeConnectors: schema.boolean({ defaultValue: true }),
   hasWebCrawler: schema.boolean({ defaultValue: true }),
   host: schema.maybe(schema.string()),

x-pack/plugins/enterprise_search/server/lib/enterprise_search_config_api.ts

@@ -53,6 +53,7 @@ export const callEnterpriseSearchConfigAPI = async ({
       features: {
         hasConnectors: config.hasConnectors,
         hasDefaultIngestPipeline: config.hasDefaultIngestPipeline,
+        hasDocumentLevelSecurityEnabled: config.hasDocumentLevelSecurityEnabled,
         hasNativeConnectors: config.hasNativeConnectors,
         hasWebCrawler: config.hasWebCrawler,
       },
@@ -106,6 +107,7 @@ export const callEnterpriseSearchConfigAPI = async ({
       features: {
         hasConnectors: config.hasConnectors,
         hasDefaultIngestPipeline: config.hasDefaultIngestPipeline,
+        hasDocumentLevelSecurityEnabled: config.hasDocumentLevelSecurityEnabled,
         hasNativeConnectors: config.hasNativeConnectors,
         hasWebCrawler: config.hasWebCrawler,
       },