Flex Gateway Instances

[soufi]

Adds the following data-sources:

• anypoint_flexgateway_target to get all flex gateway targets in a given organization
• anypoint_flexgateway_target to get a specific flex gateway target by its Id in a given organization
• anypoint_apim to list api manager instances and filter them by different criteria in a given organization and environment
• anypoint_apim_instance to get a specific api manager instance details
• anypoint_apim_instance_upstreams to list all api manager upstreams

Adds the following resources:

• anypoint_apim_flexgateway to manage an api manager instance of type flex gateway