fix(build): made protoc optional

it's unavailable on macOS arm64 (YePpHa/node-protoc#9) and the API
generation is a manual process: 0942ef6

Signed-off-by: Akos Kitta <[email protected]>

Author: Akos Kitta

Diff for: arduino-ide-extension/package.json

@@ -123,13 +123,13 @@
     "mockdate": "^3.0.5",
     "moment": "^2.24.0",
     "ncp": "^2.0.0",
-    "protoc": "^1.0.4",
     "shelljs": "^0.8.3",
     "uuid": "^3.2.1",
     "yargs": "^11.1.0"
   },
   "optionalDependencies": {
-    "grpc-tools": "^1.9.0"
+    "grpc-tools": "^1.9.0",
+    "protoc": "^1.0.4"
   },
   "mocha": {
     "require": [