storcon_cli: timeline-safekeeper-migrate and timeline-locate subcommands (#12548)

## Problem
We have a `safekeeper_migrate` handler, but no subcommand in
`storcon_cli`. Same for `/:timeline_id/locate` for identifying current
set of safekeepers.

- Closes: https://github.com/neondatabase/neon/issues/12395

## Summary of changes
- Add `timeline-safekeeper-migrate` and `timeline-locate` subcommands to
`storcon_cli`

storage_controller/src/service/safekeeper_service.rs

@@ -25,7 +25,8 @@ use pageserver_api::models::{SafekeeperInfo, SafekeepersInfo, TimelineInfo};
 use safekeeper_api::PgVersionId;
 use safekeeper_api::membership::{self, MemberSet, SafekeeperGeneration};
 use safekeeper_api::models::{
-    PullTimelineRequest, TimelineMembershipSwitchRequest, TimelineMembershipSwitchResponse,
+    PullTimelineRequest, TimelineLocateResponse, TimelineMembershipSwitchRequest,
+    TimelineMembershipSwitchResponse,
 };
 use safekeeper_api::{INITIAL_TERM, Term};
 use safekeeper_client::mgmt_api;
@@ -37,13 +38,6 @@ use utils::lsn::Lsn;
 
 use super::Service;
 
-#[derive(serde::Serialize, serde::Deserialize, Clone)]
-pub struct TimelineLocateResponse {
-    pub generation: SafekeeperGeneration,
-    pub sk_set: Vec<NodeId>,
-    pub new_sk_set: Option<Vec<NodeId>>,
-}
-
 impl Service {
     fn make_member_set(safekeepers: &[Safekeeper]) -> Result<MemberSet, ApiError> {
         let members = safekeepers