Fix/Clear endpoint_properties in policy DB if empty properties recieved in PTU

[ShobhitAd]

This PR is ready for review.

Risk

This PR makes no API changes.

Testing Plan

• Manual testing with sdl_server. Test sending PTU with endpoint_properties: {}

Summary

Currently endpoint_properties is cleared from the cache if empty in PTU, but is not cleared from the policy database.

This PR

• Adds a check for endpoint_properties.empty() in SaveServiceEndpointProperties.
• If endpoint_properties.empty(), executes a query to clear the endpoint_properties in the policy DB.

CLA

• I have signed the CLA