Add integration tests for control plane logic

[tillrohrmann]

Tasks

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1. Checking that Chain with first segment is created at startup
2. Checking that new chain segment is added once previous segment is selead
3. Checking that segment is sealed if there is risk to lose write/f-majority

[pcholakov]

I've shared a super sketchy draft PR here that shows some my current thinking: https:/restatedev/restate/pull/2045/files

It doesn't build and isn't integrated into the existing cluster scheduler; rather it takes a slightly different and more functional approach to deciding the next state + required effects if any.