pageserver: expedite tenant activation on delete (#6190)

## Problem

During startup, a tenant delete request might have to retry for many
minutes waiting for a tenant to enter Active state.

## Summary of changes

- Refactor delete_tenant into TenantManager: this is not a functional
change, but will avoid merge conflicts with
https://github.com/neondatabase/neon/pull/6105 later
- Add 412 responses to the swagger definition of this endpoint.
- Use Tenant::wait_to_become_active in `TenantManager::delete_tenant`

---------

Co-authored-by: Arpad Müller <arpad-m@users.noreply.github.com>

pageserver/src/http/openapi_spec.yml

@@ -159,6 +159,12 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/ConflictError"
+        "412":
+          description: Deletion may not proceed, tenant is not in Active state
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/PreconditionFailedError"
         "500":
           description: Generic operation error
           content:

pageserver/src/http/routes.rs

@@ -308,6 +308,7 @@ impl From<crate::tenant::delete::DeleteTenantError> for ApiError {
             SlotUpsertError(e) => e.into(),
             Other(o) => ApiError::InternalServerError(o),
             e @ InvalidState(_) => ApiError::PreconditionFailed(e.to_string().into_boxed_str()),
+            Cancelled => ApiError::ShuttingDown,
         }
     }
 }
@@ -886,7 +887,9 @@ async fn tenant_delete_handler(
 
     let state = get_state(&request);
 
-    mgr::delete_tenant(state.conf, state.remote_storage.clone(), tenant_shard_id)
+    state
+        .tenant_manager
+        .delete_tenant(tenant_shard_id, ACTIVE_TENANT_TIMEOUT)
         .instrument(info_span!("tenant_delete_handler",
             tenant_id = %tenant_shard_id.tenant_id,
             shard = %tenant_shard_id.shard_slug()