Remove empty attributes from telemetry data as part of gateway data enrichment

[a-thaler]

Description

There are backends like Dynatrace having problems with attributes and resource attributes of type string with empty values. Instead of introducing ways to remove these values specificly for some backends, the gateway should just drop them as part of the data hamonization as the usefulness of these data is questionable.

Criterias

• For data being pushed to a gatway having empty String (resource) attributes, these attributes are getting dropped
• The feature is described in the end-user documentation
• E2E tests are assuring compatibility