Support adding the same label edges with different labels in src and dst

[lidongze0629]

As title, pass the following test with an eager mode session.

# add the same label "group" edges with different src dst labels
def test_multi_src_dst_edge_loader():
    graph = graphscope_session.g()
    graph = graph.add_vertices(student_v, "student")
    graph = graph.add_vertices(teacher_v, "teacher")
    graph = graph.add_edges(
        student_group_e,
        "group",  # "group" edges with "student" src and dst
        ["group_id", "member_size"],
        src_label="student",
        dst_label="student",
    )
    graph = graph.add_edges(
        teacher_group_e,
        "group",  # "group" edges with "teacher" src and dst
        ["group_id", "member_size"],
        src_label="teacher",
        dst_label="teacher",
    )