Add minimal validation workflow

## Environment

**Package version:** N/A

## Description

**What you'd like to happen:**
Has a minimal workflow with Github actions to verify code
- Analyze static code
- Build example
- Check broken links

**Alternatives you've considered:**
Copy from [phone_number repo](https://github.com/flutter-form-builder-ecosystem/phone_number/blob/main/.github/workflows/base.yaml)