pageserver: fix stripe size persistence in legacy HTTP handlers (#12377)

## Problem

Similarly to #12217, the following endpoints may result in a stripe size
mismatch between the storage controller and Pageserver if an unsharded
tenant has a different stripe size set than the default. This can lead
to data corruption if the tenant is later manually split without
specifying an explicit stripe size, since the storage controller and
Pageserver will apply different defaults. This commonly happens with
tenants that were created before the default stripe size was changed
from 32k to 2k.

* `PUT /v1/tenant/config`
* `PATCH /v1/tenant/config`

These endpoints are no longer in regular production use (they were used
when cplane still managed Pageserver directly), but can still be called
manually or by tests.

## Summary of changes

Retain the current shard parameters when updating the location config in
`PUT | PATCH /v1/tenant/config`.

Also opportunistically derive `Copy` for `ShardParameters`.

safekeeper/src/handler.rs

@@ -220,7 +220,7 @@ impl<IO: AsyncRead + AsyncWrite + Unpin + Send> postgres_backend::Handler<IO>
                                     stripe_size: ShardStripeSize(stripe_size),
                                 };
                                 self.shard =
-                                    Some(ShardIdentity::from_params(ShardNumber(number), &params));
+                                    Some(ShardIdentity::from_params(ShardNumber(number), params));
                             }
                             _ => {
                                 return Err(QueryError::Other(anyhow::anyhow!(