OCM-7306 | feat: Added support for KubeletConfigs to HCP MachinePools

[robpblake]

This PR adds in API Model definitions for the KubeletConfig endpoints to support custom PIDs limits on HCP clusters. In this PR we add the following:

• Expose the /api/clusters_mgmt/v1/clusters/{id}/kubelet_configs endpoint that allows users to create one or more KubeletConfigs for their HCP clusters
  • For Classic Clusters, validation on this endpoint will permit the creation of a single KubeletConfig
• Expose the /api/clusters_mgmt/v1/clusters/{id}/kubelet_configs/{kubelet_config_id} endpoint that allows the user to retrieve details of the specific KubeletConfig
• Add the kubelet_configs field to the NodePool resource

[den-rgb]

/lgtm

[hunterkepley]

/lgtm