Implement endpoint to get job executions users

Steps:

• create json schema that describes information about job execution user
• define endpoint to retrieve a list of unique user DTO items
  • the endpoint should provide pagination query parameters
  • the endpoint should require "metadata-provider.jobexecutions.get" permission necessary for jobExecution retrieving
• implement a method to Dao component to retrieve list of user info DTO elements based on data from "job_execution" table
• add tests