fix(poly sync): exclude empty folders for the dev project

[DavidVujic]

Description

poly sync: exclude empty folders when adding missing bricks to the development project.

Motivation and Context

Fixes #408

How Has This Been Tested?

✅ CI
✅ local run of the poly sync command with empty bricks

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have read the code of conduct.
• I have read the contributing guide.
• I have updated the documentation accordingly (if applicable).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud