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/host_set.go

@@ -2,7 +2,6 @@ package plugin
 
 import (
 	"context"
-	"encoding/json"
 
 	"github.com/hashicorp/boundary/internal/errors"
 	"github.com/hashicorp/boundary/internal/host/plugin/store"
@@ -22,23 +21,21 @@ type HostSet struct {
 func NewHostSet(ctx context.Context, catalogId string, opt ...Option) (*HostSet, error) {
 	const op = "plugin.NewHostSet"
 	opts := getOpts(opt...)
+	attrs, err := proto.Marshal(opts.withAttributes)
+	if err != nil {
+		return nil, errors.Wrap(ctx, err, op, errors.WithCode(errors.InvalidParameter))
+	}
+
 	set := &HostSet{
 		HostSet: &store.HostSet{
 			CatalogId:          catalogId,
 			Name:               opts.withName,
 			Description:        opts.withDescription,
+			Attributes:         attrs,
 			PreferredEndpoints: opts.withPreferredEndpoints,
 		},
 	}
 
-	if opts.withAttributes != nil {
-		attrs, err := json.Marshal(opts.withAttributes)
-		if err != nil {
-			return nil, errors.Wrap(ctx, err, op, errors.WithCode(errors.InvalidParameter))
-		}
-		set.Attributes = attrs
-	}
-
 	return set, nil
 }
 
@@ -64,9 +61,13 @@ func allocHostSet() *HostSet {
 
 func (s *HostSet) clone() *HostSet {
 	cp := proto.Clone(s.HostSet)
-	return &HostSet{
+	hs := &HostSet{
 		HostSet: cp.(*store.HostSet),
 	}
+	if s.Attributes != nil && len(s.Attributes) == 0 && hs.Attributes == nil {
+		hs.Attributes = []byte{}
+	}
+	return hs
 }
 
 func (s *HostSet) oplog(op oplog.OpType) oplog.Metadata {