MM-59875: default apps enabled false (#27756)

* MM-59875: default apps enabled false

We stopped prepackaging the apps framework and stopped supporting it in
Mattermost Cloud a year ago. As part of v10, we're formally deprecating
it, while making allowances for customers who still need to transition
by not making this a breaking change immediately. To help prevent new
adoption, let's ensure the feature flag is disabled by default.

Fixes: https://mattermost.atlassian.net/browse/MM-59875

* fix tests

server/channels/app/plugin_test.go

@@ -1437,6 +1437,18 @@ func TestGetPluginStateOverride(t *testing.T) {
 	t.Run("apps override", func(t *testing.T) {
 		t.Run("without enabled flag", func(t *testing.T) {
 			overrides, value := th.App.ch.getPluginStateOverride("com.mattermost.apps")
+			require.True(t, overrides)
+			require.False(t, value)
+		})
+
+		t.Run("with enabled flag set to true", func(t *testing.T) {
+			os.Setenv("MM_FEATUREFLAGS_APPSENABLED", "true")
+			defer os.Unsetenv("MM_FEATUREFLAGS_APPSENABLED")
+
+			th2 := Setup(t)
+			defer th2.TearDown()
+
+			overrides, value := th2.App.ch.getPluginStateOverride("com.mattermost.apps")
 			require.False(t, overrides)
 			require.False(t, value)
 		})

server/public/model/feature_flags.go

@@ -61,7 +61,7 @@ func (f *FeatureFlags) SetDefaults() {
 	f.TestFeature = "off"
 	f.TestBoolFeature = false
 	f.EnableRemoteClusterService = false
-	f.AppsEnabled = true
+	f.AppsEnabled = false
 	f.NormalizeLdapDNs = false
 	f.CallsEnabled = true
 	f.DeprecateCloudFree = false