Add mojo-dotenv v0.2.2 - .env file loader for Mojo

[Mjboothaus]

Adds mojo-dotenv v0.2.2 - Production-ready .env file parser and loader for Mojo.

Changes from previous PR #192:

• ✅ Added package image (recipes/mojo-dotenv/image.png) for builds.modular.com display per reviewer guidelines
• ✅ Enabled CodeQL scanning and added badge to repository README
• ✅ Updated license to Apache-2.0
• ✅ Bumped to v0.2.2 to mark this enhanced release
• ✅ Renamed test file to test_package.mojo per convention

Package features:

• Parse .env files to Dict or load into environment
• Variable expansion (${VAR} and $VAR syntax)
• Multiline values and escape sequences
• Auto-discovery with find_dotenv()
• 98%+ compatible with python-dotenv
• 49 comprehensive tests using Mojo's TestSuite framework
• Zero Python dependencies

Use case: Following 12-factor app methodology for configuration management in Mojo applications.

Repository: https://github.com/DataBooth/mojo-dotenv
CodeQL:

Supersedes #192