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/host/plugin/immutable_fields_test.go

@@ -10,6 +10,7 @@ import (
 	"github.com/hashicorp/boundary/internal/iam"
 	"github.com/hashicorp/boundary/internal/kms"
 	"github.com/hashicorp/boundary/internal/plugin/host"
+	plgpb "github.com/hashicorp/boundary/sdk/pbs/plugin"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"google.golang.org/protobuf/proto"
@@ -101,7 +102,9 @@ func TestPluginSet_ImmutableFields(t *testing.T) {
 	_, prj := iam.TestScopes(t, iam.TestRepo(t, conn, wrapper))
 	plg := host.TestPlugin(t, conn, "test", "prefix")
 	cat := TestCatalog(t, conn, prj.PublicId, plg.GetPublicId())
-	new := TestSet(t, conn, kmsCache, cat)
+	new := TestSet(t, conn, kmsCache, cat, map[string]plgpb.HostPluginServiceServer{
+		plg.GetPublicId(): &TestPluginServer{},
+	})
 
 	tests := []struct {
 		name      string