Standardize Cluster Resources Collector

[xavpaice]

Per the design in #893, this task is to make the following changes in preparation for integrating sbctl to the Troubleshoot repo:

• In pkg/collect standardize the root directory location of the Cluster Resources collector with a variable instead of repeatedly specifying it as a string - https://github.com/replicatedhq/troubleshoot/blob/main/pkg/collect/cluster_resources.go#L121.
• Import the directory the Cluster Resources collector uses from pkg/collect for usage in the APIs - https://github.com/replicatedhq/sbctl/blob/main/pkg/api/server.go#L220. This is an example of the way we can start making the sbctl code more efficient with this change.

Definition of done:

• clusterResources specifies the root directory as a var in pkg/collect (use package constants for the source)
• sbctl pkg/api/server.go imports Troubleshoot's constants package and uses that to determine the file locations