Use query params instead of hardcoded values in node expansion query

[cqian23]

We are using triple single quotes to safely escape query param values when running node expansion query:

• spanner-graph-notebook/spanner_graphs/graph_server.py

  Line 191 in 7a0da83

  value_str = f"\'''{node_property.value}\'''"

We should fix it by using query params of data value + data type like here: https://cloud.google.com/spanner/docs/getting-started/python#query_using_a_sql_parameter

On types and values of params:

• Type: today, type info is already sent to python side in node_property.type_str: https://cloud.google.com/spanner/docs/getting-started/python#query_using_a_sql_parameter.
• Value: we can simply cast them into python data types and put them in a dict