Extend json-specs tests with cgroup-parsing

[z1c0]

This is a follow-up of #678 as suggested by @felixbarny in #678 (comment).
The existing tests in apm-agent-dotnet served as the source for these json-specs test data.
Once this PR is merged, apm-dotnet-agent will also switch to using json-specs as input (FYI @gregkalapos).

[apmmachine]

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• Start Time: 2022-09-26T04:25:00.932+0000

• Duration: 7 min 4 sec

[SylvainJuge]

There are also quite a lot of other variants in Java agent test: https://github.com/elastic/apm-agent-java/blob/e9aacfdd2551dd52baae5881079c8597ea3d8cca/apm-agent-core/src/test/java/co/elastic/apm/agent/impl/metadata/ContainerInfoTest.java#L31

We could however add those in a follow-up PR when the Java agent has automated tests with this new JSON specification, but maybe if there are other parsed attributes it could be relevant to look at those too.

[z1c0]

There are also quite a lot of other variants in Java agent test: elastic/apm-agent-java@e9aacfd/apm-agent-core/src/test/java/co/elastic/apm/agent/impl/metadata/ContainerInfoTest.java#L31

We could however add those in a follow-up PR when the Java agent has automated tests with this new JSON specification, but maybe if there are other parsed attributes it could be relevant to look at those too.

Agreed, that sounds like a good follow-up once this PR is through.

[z1c0]

Hi @SylvainJuge are you fine with the PR in its current state or would you expect further changes?
Thanks, Wolfgang

[SylvainJuge]

LGTM, follow-up issues/PRs are expected once agents add those tests in their respective codebases.