Add granular permissions for secondary owners

[kjlippold]

Describe the feature you'd like and what it will do

API Keys should be decoupled from permissions, and permissions should be assignable to secondary owners by primary owners.

Why is this feature important?

Secondary owners currently have most of the same privileges of primary owners, and cannot be customized in any way. Giving primary owners the ability to control the permissions of secondary owners would let them safely allow secondary owners to perform certain tasks without having almost full access to a Thing.

Is your feature request related to a problem? Please describe.

No response

Any additional comments?

This feature could be combined with owner roles #110. Rather than (or in addition to) assigning permissions to users, permissions could be created for roles, and roles could be assigned to users. This would make it easier to define complex permissions one time and reuse them for multiple users/Things.

This shouldn't need to be as complex as AWS or GCP IAM, but those could serve as a template for what HydroServer needs.