debug: Launch custom commands from start modal (#32484)

Release Notes:

- Add custom command launching from the `debug: start` modal

---------

Co-authored-by: Anthony Eid <hello@anthonyeid.me>

assets/settings/default.json

@@ -1478,7 +1478,8 @@
     "Go": {
       "code_actions_on_format": {
         "source.organizeImports": true
-      }
+      },
+      "debuggers": ["Delve"]
     },
     "GraphQL": {
       "prettier": {
@@ -1543,9 +1544,15 @@
     "Plain Text": {
       "allow_rewrap": "anywhere"
     },
+    "Python": {
+      "debuggers": ["Debugpy"]
+    },
     "Ruby": {
       "language_servers": ["solargraph", "!ruby-lsp", "!rubocop", "!sorbet", "!steep", "..."]
     },
+    "Rust": {
+      "debuggers": ["CodeLLDB"]
+    },
     "SCSS": {
       "prettier": {
         "allowed": true