Update task defaults (#28368)

Follow-up of https://github.com/zed-industries/zed/pull/28359

Release Notes:

- N/A

assets/settings/default.json

@@ -1136,7 +1136,8 @@
   "code_actions_on_format": {},
   // Settings related to running tasks.
   "tasks": {
-    "variables": {}
+    "variables": {},
+    "enabled": true
   },
   // An object whose keys are language names, and whose values
   // are arrays of filenames or extensions of files that should
@@ -1456,6 +1457,8 @@
   "lsp": {
     // Specify the LSP name as a key here.
     // "rust-analyzer": {
+    //     // A special flag for rust-analyzer integration, to use server-provided tasks
+    //     enable_lsp_tasks": true,
     //     // These initialization options are merged into Zed's defaults
     //     "initialization_options": {
     //         "check": {