Import external dependencies with the import map

[zimeg]

Type of change

• [ ] New sample
• [x] New feature
• [ ] Bug fix
• [ ] Documentation

Summary

This PR moves module imports into the import_map.json file for easier updating.

Notes

• An update to the deno-sample-dependencies repo will follow!

Requirements

• [x] I’ve checked my submission against the Samples Checklist to ensure it complies with all standards
• [x] I have ensured the changes I am contributing align with existing patterns and have tested and linted my code
• [x] I've read and agree to the Code of Conduct

[zimeg]

@filmaj appreciate the reviews - thank you! 🕺