Add first set of Chaos Tests

What does this MR do and why?

Part of #368586

Documentation relating to using the Test::Integration::Chaos Scenario under Test::Instance::Chaos

Add first set of chaos tests.
These tests focus on validating that the behaviour of basic git operations via the UI are not negatively impacted if gitaly/praefect nodes are experiencing some network connectivity issues.

Future iterations of these tests can delve further into the expected outcomes and other environmental networking issues.

MR acceptance checklist

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