Move API resource pbs to new location (#1484)

This moves the generated pb files to the `sdk` module. This allows third parties to make use of them if desired (e.g. in upcoming plugins) and moves away from the `gen` nomenclature in the directory, since we are going to be adding some extra interface functions to the messages.

internal/servers/controller/common/scopeids/scope_ids.go

@@ -4,7 +4,6 @@ import (
 	"context"
 
 	"github.com/hashicorp/boundary/internal/errors"
-	"github.com/hashicorp/boundary/internal/gen/controller/api/resources/scopes"
 	"github.com/hashicorp/boundary/internal/iam"
 	"github.com/hashicorp/boundary/internal/perms"
 	"github.com/hashicorp/boundary/internal/servers/controller/auth"
@@ -13,6 +12,7 @@ import (
 	"github.com/hashicorp/boundary/internal/types/action"
 	"github.com/hashicorp/boundary/internal/types/resource"
 	"github.com/hashicorp/boundary/internal/types/scope"
+	"github.com/hashicorp/boundary/sdk/pbs/controller/api/resources/scopes"
 )
 
 // GetListingScopeIds, given common parameters for List calls, returns the set of scope