[Aikido] Add 1 packages.lock.json file for dependency locking

[aikido-autofix-us]

.NET Lockfile Creation

This PR adds packages.lock.json files to ensure reproducible builds and secure dependency management.

Files Added:

• services/windows-dropbox-service/packages.lock.json

Benefits:

• Reproducible builds: Locked dependency versions ensure consistent builds across environments
• Security: Prevents supply chain attacks by pinning specific dependency versions
• Performance: Faster builds in CI/CD pipelines
• Deterministic child dependency scanning: Scanning for child dependencies becomes deterministic, reducing false positives in dependency analysis

The lockfiles were generated using dotnet restore command.