Add usageType to permissions required fields list in schema 2.0

[froi]

Expected Behavior

The validation tool should give out an error for every release/repo that does not have a value for the usageType field in the permissions property.

Current Behavior

No error is being shown when usageType is being omitted.

Possible Solution

Add usageType field to the required list for the permissions property.

Steps to Reproduce (for bugs)

1. Copy the following code.json
2. Go to Code.gov's validation tool
3. Paste the code.json into the validation editor.
4. Look at the results under the validation editor.

Context

The validation tool is giving faulty results.