[OGUI-1832] Filter out empty detectors reported by apricot

[graduta]

I have JIRA issue created

• branch and/or PR name(s) includes JIRA ID
• issue has "Fix version" assigned
• issue "Status" is set to "In review"
• PR labels are selected
• FLP integration tests were ran successful

PR which:

• extracts functionality of fetching detectors from Apricot (and keeping them in memory) to a dedicated detectors service
• this higer-level service also filters out any whitespaces only or empty detectors as reported by Apricot due to Consul Bug.
• adds unit tests and API integration tests for updated functionality