develop the process to store function_schemas in the vectorDB during the initialization of route_layer

This reverts commit 7597bc35.

The former is only supported from Python 3.10 onwards and we'd like to support Python 3.9 onwards.

Mostly just trying to make MyPy happy!

It's defined in the BaseIndex which LocalIndex inherits anyway

Also fixed bug in layer.py where we weren't:
a) Setting the index_name to a default value.
b) Weren't using index_name.

Making pydantic leave me alone and giving the correct index name.

Also made sure it's used properly in layer.py.