release-25.3: server: return draining progress if the server controller is draining

[iskettaneh]

Backport 1/1 commits from #155063.

/cc @cockroachdb/release

---

This commit fixes a bug where if the server controller is being drained, the drain command would return a response without populating the IsDraining. The CLI interprets this as if the draining is completed.

server: return draining progress if the server controller is draining

This commit fixes a bug where if the server controller is being drained, the drain command would return a response without populating the IsDraining field. The CLI interprets this as if the draining is completed.

Output example when running:

./cockroach node drain 3 --insecure --url {pgurl:3} --logtostderr=INFO

I251008 15:54:42.613200 15 2@rpc/peer.go:613  [rnode=?,raddr=10.142.1.228:26257,class=system,rpc] 1  connection is now healthy
node is draining... remaining: 3
I251008 15:54:42.622586 1 cli/rpc_node_shutdown.go:184  [-] 2  drain details: tenant servers: 3
node is draining... remaining: 3
I251008 15:54:42.824526 1 cli/rpc_node_shutdown.go:184  [-] 3  drain details: tenant servers: 3
node is draining... remaining: 1
I251008 15:54:43.026405 1 cli/rpc_node_shutdown.go:184  [-] 4  drain details: tenant servers: 1
node is draining... remaining: 1
I251008 15:54:43.228596 1 cli/rpc_node_shutdown.go:184  [-] 5  drain details: tenant servers: 1
node is draining... remaining: 243
I251008 15:54:44.580413 1 cli/rpc_node_shutdown.go:184  [-] 6  drain details: liveness record: 1, range lease iterations: 175, descriptor leases: 67
node is draining... remaining: 0 (complete)
drain ok

Release note (bug fix): fixed a bug in the drain command where draining a node using virtual clusters (such as clusters running Physical Cluster Replication) could return before the drain was complete, possibly resulting in shutting down the node while it still had active SQL clients and ranges leases.

Epic: None

Release justification: need to backport a bug fix to draining where we used to not fully drain nodes when using virtual clustters.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that the change does not break backwards compatibility and otherwise complies with the backport policy. Include a brief release justification in the PR description explaining why the backport is appropriate. All backports must be reviewed by the TL for the owning area. While the stricter LTS policy does not yet apply, please exercise judgment and consider gating non-critical changes behind a disabled-by-default feature flag when appropriate.

[cockroach-teamcity]

This change is 

[celiala]

blathers backport staging-v25.3.4