[FEATURE REQUEST] Adjust automated tests to Filebeat v7.8.1

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Is your feature request related to a problem? Please describe.
Starting with 7.0, the fields exported by Beats conform to the Elastic Common Schema (ECS). Many of the exported fields have been renamed. See Breaking changes in 7.0 for the full list of changed names.

After implementing #846 automated tests fail due to the breaking changes.

Describe the solution you'd like
No Filebeat related failing tests for builds from develop branch.

Describe alternatives you've considered
Try with enabling the compatibility layer for Elastic Common Schema (ECS) fields, see here.

Additional context
The failing tests are in postgresql group. We need to change the source field to log.file.path.