Placeholder Plugin Providers for Repos and added testPlugin struct (#1532)

* Create minimalistic plugin map and test plugin.

* Pass secrets and attributes to the plugin when creating catalogs or sets.  Add tests for CreateSet and CreateCatalog repo methods.

* make fmt and extract out getPrivateCatalog and getCatalog helper methods.

* Exporting TestPluginServer so it can be used in the handlers.

* Keep separate persisted data from host catalogs lookups which facilitate passing it onto the plugins.

* Add TODO to merge get Catalog and get Persisted data.

* Adding tests for unimplemented being returned by the plugin.

* Use GetFields() instead of AsMap() to confirm attributes should be populated. Make clone consistent between catalog and sets.

Co-authored-by: Jeff Mitchell <jeffrey.mitchell@gmail.com>

internal/db/schema/migrations/postgres/17/04_plugin_host.up.sql

@@ -54,9 +54,7 @@ begin;
     create_time wt_timestamp,
     update_time wt_timestamp,
     version wt_version,
-    attributes bytea not null
-      constraint attributes_must_not_be_empty
-      check(length(attributes) > 0),
+    attributes bytea not null,
     constraint host_catalog_fkey
     foreign key (scope_id, public_id)
       references host_catalog (scope_id, public_id)
@@ -126,9 +124,7 @@ begin;
     create_time wt_timestamp,
     update_time wt_timestamp,
     version wt_version,
-    attributes bytea not null
-      constraint attributes_must_not_be_empty
-        check(length(attributes) > 0),
+    attributes bytea not null,
     constraint host_plugin_set_catalog_id_name_uq
     unique(catalog_id, name),
     constraint host_set_fkey