[#546] Only network tests filtering for Nettest

Description

Problem: Currently, one has to provide quite a complex pattern to run only network tests within the nettest test-suite. This is not very convenient because e.g. different CIs handle $ variables differently.

Solution: Add --nettest-run-only-network option that applies the same pattern to the test tree but does this using the pattern which is created using tasty eDSL.

Related issue(s)

Resolves #546 (closed)

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