Allow "allowed methods" to be configurable in the Distribution Behavior

[skyzyx]

I would love to be able to specify which methods are allowed for my distribution. It would be wonderful if this were configurable via this plugin.

See:

• https://github.com/Droplr/serverless-api-cloudfront/blob/master/resources.yml#L29-L36
• AllowedMethods