Sync files via CLI

[robinsowell]

Would be really nice if you could sync files via CLI, which can be really slow in CP. Two separate situations:

1. Typical directory sync, especially after you've added new image sizes and such.
2. After upgrade sync where you want to turn compatibility mode off and have a ton of files that need to be changed. This can take forever with big directories.

[intoeetive]

2 is already imlemented in sync:file-usage command
1 is getting added in this PR: #3615