kvprober: use a raft noop command in place of real writes

**Is your feature request related to a problem? Please describe.**

Currently, kvprober has the ability to write into a range, which exercises the relevant parts of the system to be able to ascertain whether the range is healthy or not, in terms of write availability.

One issue with this approach is that there exists a risk that the writes can interfere with user data. Indeed, this was observed in #101549.

**Describe the solution you'd like**

Switch to using Raft noop writes, similar to how the replica circuit breakers work. This avoids writing actual data to the range.

**Describe alternatives you've considered**

Keep things the way they are and rely on test coverage to ensure that writes aren't interacting adversely with user data.

Jira issue: CRDB-28159