pageserver: stabilize & refine controller scale test (#8971)

## Problem

We were seeing timeouts on migrations in this test.

The test unfortunately tends to saturate local storage, which is shared
between the pageservers and the control plane database, which makes the
test kind of unrealistic. We will also want to increase the scale of
this test, so it's worth fixing that.

## Summary of changes

- Instead of randomly creating timelines at the same time as the other
background operations, explicitly identify a subset of tenant which will
have timelines, and create them at the start. This avoids pageservers
putting a lot of load on the test node during the main body of the test.
- Adjust the tenants created to create some number of 8 shard tenants
and the rest 1 shard tenants, instead of just creating a lot of 2 shard
tenants.
- Use archival_config to exercise tenant-mutating operations, instead of
using timeline creation for this.
- Adjust reconcile_until_idle calls to avoid waiting 5 seconds between
calls, which causes timelines with large shard count tenants.
- Fix a pageserver bug where calls to archival_config during activation
get 404

storage_controller/src/service.rs

@@ -246,6 +246,11 @@ fn passthrough_api_error(node: &Node, e: mgmt_api::Error) -> ApiError {
             // storage controller's auth configuration.
             ApiError::InternalServerError(anyhow::anyhow!("{node} {status}: {msg}"))
         }
+        mgmt_api::Error::ApiError(status @ StatusCode::TOO_MANY_REQUESTS, msg) => {
+            // Pass through 429 errors: if pageserver is asking us to wait + retry, we in
+            // turn ask our clients to wait + retry
+            ApiError::Conflict(format!("{node} {status}: {status} {msg}"))
+        }
         mgmt_api::Error::ApiError(status, msg) => {
             // Presume general case of pageserver API errors is that we tried to do something
             // that can't be done right now.