Support multiple plugins of same type on Ingress and Service

[hbagdi]

Problem

Currently, a KongPlugin of one type can be added once to an Ingress/Service. There are use-cases when multiple such plugins, for a combination of a Route and Consumer need to be instantiated.

Solution

Add support for multiple plugins of the same type in plugins.konghq.com annotation.
#250 will also solve problems for cases when a plugin needs to be instantiated at a consumer level and not for a combination of a Consumer and Service.

The solution requires Kong/deck#13 to be implemented first, which can then be leveraged by the Ingress Controller to make this possible for database-backed deployments.

[hbagdi]

An update:

Kong Ingress Controller 0.5.0 brings in support for configuring Consumer-level plugins in Kong which solves part of this problem.

There could be use-cases which require Kong to be configured with a plugin for a specific consumer and route or a consumer and a service and this is not possible as of today.

[hbagdi]

This is now possible with 0.7.0 version.