[feat] cors plugin add a config field: override_origin

[WALL-E]

A boolean value that instructs the plugin to set the config.origins from request headers "Origin" as the value.

The user has the ability to turn off this feature.

https://github.com/Mashape/kong/blob/master/kong/plugins/cors/handler.lua#L69L82

[p0pr0ck5]

@WALL-E would you consider submitting a PR for this functionality?

[WALL-E]

@p0pr0ck5 OK