add operation id to documentation

[weierophinney]

I added this field to be able to personalized methods of the sdks generated with swagger-codegen and zf-apigility-documentation-swagger.

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Originally posted by @garygitton at zfcampus/zf-apigility-documentation#70

[weierophinney]

Note: depends on zfcampus/zf-apigility-admin#393

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Originally posted by @weierophinney at zfcampus/zf-apigility-documentation#70 (comment)