APICAST_PATH_ROUTING_ONLY is not part of the configurations options available in the APIcast operator reference document.

When trying to add it manually to the APIcast deployment it works on embedded APIcast gateways that are built in the 3scale API Manager installation. However, when trying to do the same in a self-managed APIcast, after a few seconds, the APIcast operator reconciles the change done in the apicast deployment yaml file and hence, the APICAST_PATH_ROUTING_ONLY cannot be enabled in self-managed apicast gateway.

Current behavior:

APICAST_PATH_ROUTING_ONLY can be successfully enabled in the embedded apicast gateways (3scale Operator) but it cannot be enabled in a self-managed apicast (APIcast operator) since the operator reconciles the change done in the apicast's deployment when trying to manually add it as a new environment variable.

Desired behavior:

Be able to enabled APICAST_PATH_ROUTING_ONLY in self-managed apicast gateways also.

Reproducer steps:
1) Install APIcast 2.15 operator.
2) Create an instance of apicast gateway.
3) Modify the deployment yaml of the apicast instance by adding APICAST_PATH_ROUTING_ONLY = true as new environment variable.
4) Wait for some seconds and that new variable will be deleted when APIcast operator reconciles the deployment.