pageserver/storcon: add patch endpoints for tenant config metrics (#10020)

## Problem

Cplane and storage controller tenant config changes are not additive.
Any change overrides all existing tenant configs. This would be fine if
both did client side patching, but that's not the case.

Once this merges, we must update cplane to use the PATCH endpoint.

## Summary of changes

### High Level

Allow for patching of tenant configuration with a `PATCH
/v1/tenant/config` endpoint.
It takes the same data as it's PUT counterpart. For example the payload
below will update `gc_period` and unset `compaction_period`. All other
fields are left in their original state.
```
{
  "tenant_id": "1234",
  "gc_period": "10s",
  "compaction_period": null
}
```

### Low Level
* PS and storcon gain `PATCH /v1/tenant/config` endpoints. PS endpoint
is only used for cplane managed instances.
* `storcon_cli` is updated to have separate commands for
`set-tenant-config` and `patch-tenant-config`

Related https://github.com/neondatabase/cloud/issues/21043

pageserver/pagebench/src/cmd/aux_files.rs

@@ -64,7 +64,7 @@ async fn main_impl(args: Args) -> anyhow::Result<()> {
     println!("operating on timeline {}", timeline);
 
     mgmt_api_client
-        .tenant_config(&TenantConfigRequest {
+        .set_tenant_config(&TenantConfigRequest {
             tenant_id: timeline.tenant_id,
             config: TenantConfig::default(),
         })