CLI #100 — Add a --no-update-check flag to disable the update notification

## Task
Add a `--no-update-check` global flag and a `updateCheck: false` config file option to opt out of the startup version check.

## Files to update
```
packages/cli/src/index.ts
packages/cli/src/lib/updateCheck.ts
packages/cli/src/lib/configFile.ts
```