chore: Increase default concurrency for plugin dev (#1270)

The default concurrency value for `lerna` is to use the number of
logical cores. In cases where the number of logical cores is < the
number of plugins, `npm start:packages` will only build some of the
plugins.

For example, on my Mac, I have 10 logical cores, and we now have 11
plugins. This resulted in `ui` plugin not being built.

This PR increases the default to 20 which gives us some cushion to grow
in the number of plugins.

## Testing
I have tested this by running `npm start` on my machine which has 10
logical cores. All 11 plugins ran in watch mode. Without the
`--concurrency 20` flag, only 10 of them run.

Author: bmingles

package.json

@@ -12,7 +12,7 @@
     "types": "tsc",
     "watch:types": "tsc --watch",
     "serve:plugins": "vite",
-    "start:packages": "lerna run start --stream",
+    "start:packages": "lerna run start --stream --concurrency 20",
     "docs": "./tools/run_docker.sh ./docker-compose.docs.yml docs",
     "test": "jest --watch --changedSince origin/main",
     "test:unit": "jest --config jest.config.unit.cjs",