feat(group): group service to create, update, and delete groups (#10455)

# Which Problems Are Solved

This PR adds API definition and backend implementation for GroupService
to manage user groups.

# How the Problems Are Solved
* API definition to create, update, retrieve, and delete groups is added
* Command-side implementation to create, update, and delete user groups
as part of the GroupV2 API is added

# Additional Changes
N/A

# Additional Context
- Related to #10089, #9702 (parent ticket)
- User contribution: https://github.com/zitadel/zitadel/pull/9428/files
- Additional functionalities to list/search user groups, add
permissions, manage users in groups, group scopes will be added in
subsequent PRs.
- Also needs documentation, which will be added once the entire feature
is available

---------

Co-authored-by: Livio Spring <[email protected]>

internal/api/grpc/group/v2/query.go

@@ -0,0 +1,45 @@
+package group
+
+import (
+	"context"
+
+	"connectrpc.com/connect"
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	"github.com/zitadel/zitadel/internal/query"
+	"github.com/zitadel/zitadel/internal/zerrors"
+	group "github.com/zitadel/zitadel/pkg/grpc/group/v2"
+)
+
+// GetGroup returns a group that matches the group ID in the request
+func (s *Server) GetGroup(ctx context.Context, req *connect.Request[group.GetGroupRequest]) (*connect.Response[group.GetGroupResponse], error) {
+	return nil, zerrors.ThrowUnimplemented(nil, "GRP-1234", "Errors.Internal.Unimplemented")
+}
+
+// ListGroups returns a list of groups that match the search criteria
+func (s *Server) ListGroups(ctx context.Context, req *connect.Request[group.ListGroupsRequest]) (*connect.Response[group.ListGroupsResponse], error) {
+	resp, err := s.query.SearchGroups(ctx)
+	if err != nil {
+		return nil, err
+	}
+	return connect.NewResponse(&group.ListGroupsResponse{
+		Groups: groupsToPb(resp.Groups),
+	}), nil
+}
+
+func groupsToPb(groups []*query.Group) []*group.Group {
+	pbGroups := make([]*group.Group, len(groups))
+	for i, g := range groups {
+		pbGroups[i] = groupToPb(g)
+	}
+	return pbGroups
+}
+
+func groupToPb(g *query.Group) *group.Group {
+	return &group.Group{
+		Id:           g.ID,
+		Name:         g.Name,
+		CreationDate: timestamppb.New(g.CreationDate),
+		ChangeDate:   timestamppb.New(g.ChangeDate),
+	}
+}