Background:We agreed to allow system/tenant users to be specified declaratively in module descriptors.  The manager components would be responsible for creating the users and assigning the appropriate roles/capabilities.  However, modules (mod-search, mod-pubsub, etc.) have not yet been updated to remove/disable the code which creates and manages system users.  This system user creation by the modules is causing problems for the FSE team since these modules expect mod-permissions to be available so permissions can be assigned to the newly created system users.   As it turns out we still have mod-permissions in the system.  We need it for migration purposes.  However, mod-permissions' tenant-permissions API is not being called by any of our components (it is called by OKAPI on the legacy platform).  This means that when modules try to assign permissions to their system users, in some cases (e.g. a fresh system) mod-permissions is unaware that those permissions even exist. The decision was made to add an environment var should be added to the modules which conditionalizes the relevant code (For creation, mgmt, and use of system users). This work will be done in the community repositories as feature branches, and will not be merged to master until Eureka code is open sourced. Purpose:This functionality is implemented for the RMB-based mod-pubsub in scope of US1182725: mod-pubsub - add support for disabling system user creation/mgmt/use.  This story is to implement the same functionality in the RMB-based mod-erm-usage-harvester. Scope:Implement the ability to conditionally create/manage/use system users (controlled via environment variable) in mod-erm-usage-harvesterUpdate tests and README as neededThis work is planned to happen after the Eureka code has been open-sourced, so it can be handled in a standard way, being merged to master instead of a long-lived feature branch.