Enhance etcd raft TLA+ spec

[joshuazh-x]

This PR is separated from the original PR #204. It includes following changes.

1. Add ready phase to the spec to model state persistence in etcd implementation.
2. Add more trace points in raft module to facilitate trace validation.
3. Improve spec hierarchy to decouple model checking and trace validation spec from the main spec

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: joshuazh-x
Once this PR has been reviewed and has the lgtm label, please assign serathius for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[joshuazh-x]

cc @serathius @ahrtr @lemmy @zeu5

This PR contains spec changes in #204 as suggested by @ahrtr .

[serathius]

It might be to daunting to review 1000 lines of code. Any way to cut it into smaller pieces?

[k8s-ci-robot]

PR needs rebase.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.