Add function register_query_handler_inside_udf

[ckunki]

Acceptance Criteria

• The register function e.g. register_query_handler_inside_udf() is added to AAF python code
• The register function should add the udf to module exasol_advanced_analytics_framework.custom, so we need to add an empty module at this place
• The register function is included in the adhoc example of the user guide incl. a comment that it only needs to be called when defining the query handler inside of a UDF (= adhoc)

[tkilias]

the register_query_handler_inside_udf function should add the udf to module exasol_advanced_analytics_framework.custom, so we need to add an empty module at this place