Add CORS pre-flight OPTIONS endpoints

[jonathan-r-thorpe]

OPTIONS is already specified in other NMOS specifications (including IS-04, IS-05, IS-08) with a clause that covers all NMOS specifications:

"In order to permit web-based control interfaces to be hosted remotely, all NMOS APIs MUST implement valid CORS HTTP headers in responses to all requests. In addition to this, where highlighted in the API specifications servers MUST respond to HTTP pre-flight OPTIONS requests. Servers MAY additionally support HTTP OPTIONS requests made to any other API resource."

This pull request:

• Changes "bulkProperties" OPTIONS endpoint to PATCH
• Adds pre-flight CORS OPTIONS to the "bulkProperties" endpoint
• Adds pre-flight CORS OPTIONS "value" endpoint
• Adds pre-flight CORS OPTIONS "methods" endpoint