(5/5) [nexus] Implement Affinity/Anti-Affinity Groups in external API (#7447)

Pulled out of #7076

This PR is a partial implementation of RFD 522

It adds:
- Affinity and Anti-Affinity groups, contained within projects. These
groups are configured with a **policy** and **failure domain** can
currently contain zero or more **members**. Affinity groups attempt to
co-locate members, anti-affinity groups attempt to avoid co-locating
members.
- **Policy** describes "what to do if we cannot fulfill the co-location
request". Currently, these options are "fail" (reject the request) or
"allow" (continue with provisioning of the group member regardless).
- **Failure Domain** describes the scope of what is considered
"co-located". In this PR, the only option is "sled", but in the future,
this may be expanded to e.g. "rack".
- **Members** describe what can be added to affinity/anti-affinity
groups. In this PR, the only option is "instance". RFD 522 describes how
"anti-affinity groups may also contain affinity groups" -- which is why
this "member" terminology is introduced -- but it is not yet
implemented.
- (anti-)Affinity groups are exposed by the API, through a CRUD
interface
- (anti-)Affinity groups are considered during "sled reservation", where
instances are placed on a sled. This is most significantly implemented
(and tested) within `nexus/db-queries/src/db/datastore/sled.rs`, within
#7446

Fixes #1705

Author: smklein

common/src/api/external/http_pagination.rs

@@ -312,6 +312,19 @@ pub type PaginatedByNameOrId<Selector = ()> = PaginationParams<
 pub type PageSelectorByNameOrId<Selector = ()> =
     PageSelector<ScanByNameOrId<Selector>, NameOrId>;
 
+pub fn id_pagination<'a, Selector>(
+    pag_params: &'a DataPageParams<Uuid>,
+    scan_params: &'a ScanById<Selector>,
+) -> Result<PaginatedBy<'a>, HttpError>
+where
+    Selector:
+        Clone + Debug + DeserializeOwned + JsonSchema + PartialEq + Serialize,
+{
+    match scan_params.sort_by {
+        IdSortMode::IdAscending => Ok(PaginatedBy::Id(pag_params.clone())),
+    }
+}
+
 pub fn name_or_id_pagination<'a, Selector>(
     pag_params: &'a DataPageParams<NameOrId>,
     scan_params: &'a ScanByNameOrId<Selector>,