[api][runtime] Introduce long-term memory in python

[wenjin272]

Linked issue: #331

Purpose of change

Introduce the long-term memory interface in python, and provide an implementation based on chroma.

This is the first pr of three to introduce long-term memory in python:

1. interface and one implementation
2. support using long-term memory in action
3. async interface and execution

Tests

Unit test

API

Yes, add long-term memory related api.

Documentation

• [x] doc-needed