Enhance SnapshotResiliencyTests (elastic#49514)

A few enhancements to `SnapshotResiliencyTests`:
1. Test running requests from random nodes in more spots to enhance coverage (this is particularly motivated by elastic#49060 where the additional number of cluster state updates makes it more interesting to fully cover all kinds of network failures)
2. Fix issue with restarting only master node in one test (doing so breaks the test at an incredibly low frequency, that becomes not so low in elastic#49060 with the additional cluster state updates between request and response)
3. Improved cluster formation checks (now properly checks the term as well when forming cluster) + makes sure all nodes are connected to all other nodes (previously the data nodes would at times not be connected to other data nodes, which was shaken out now by adding the `client()` method
4. Make sure the cluster left behind by the test makes sense by running the repo cleanup action on it (this also increases coverage of the repository cleanup action obviously and adds the basis of making it part of more resiliency tests)