FEATURE: Make experimental hashtag autocomplete default for new sites (#19681)

This feature is stable enough now to make it the default going forward
for new sites. Existing sites that have not yet set enable_experimental_hashtag_autocomplete
to `true` will have it set to `false` for their site settings, which was the old default.

c.f https://meta.discourse.org/t/hashtags-are-getting-a-makeover/248866

app/assets/javascripts/discourse/tests/acceptance/hashtags-test.js

@@ -8,7 +8,10 @@ import { test } from "qunit";
 
 acceptance("Category and Tag Hashtags", function (needs) {
   needs.user();
-  needs.settings({ tagging_enabled: true });
+  needs.settings({
+    tagging_enabled: true,
+    enable_experimental_hashtag_autocomplete: false,
+  });
   needs.pretender((server, helper) => {
     server.get("/hashtags", () => {
       return helper.response({

config/site_settings.yml

@@ -2035,7 +2035,7 @@ developer:
     default: true
     client: true
   enable_experimental_hashtag_autocomplete:
-    default: false
+    default: true
     client: true
   experimental_hashtag_search_result_limit:
     default: 20

db/migrate/20230103004613_make_experimental_hashtag_feature_default_for_new_sites.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class MakeExperimentalHashtagFeatureDefaultForNewSites < ActiveRecord::Migration[7.0]
+  def up
+    execute(<<~SQL)
+      INSERT INTO site_settings (name, data_type, value, created_at, updated_at)
+      VALUES ('enable_experimental_hashtag_autocomplete', 5, 'f', now(), now())
+      ON CONFLICT DO NOTHING
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end