Fix Milvus as a long-term memory backend.

[wangxuqi]

Hi, there
As I mentioned in 1515, There are some bugs with Milvus long-term memory. This pull request is try to refactor and fix it.

Background

The enable milvus as memory backend leads some bugs and the code even not worked.

• incorrect package import path
• wrong memory implement directory
• wrong interface implement
• no tests

Changes

• fix import path of milvus.py.
• move milvus.py from script/memory to autogpt/memory/, put all memory implements together.
• add unit and integration tests.
• implement clear function correctly.

Documentation

As I explained above.

Test Plan

All unit test and integration test passed

============================= test session starts ==============================
collecting ... collected 5 items

milvus_memory_test.py::TestMilvusMemory::test_add 
milvus_memory_test.py::TestMilvusMemory::test_clear 
milvus_memory_test.py::TestMilvusMemory::test_get 
milvus_memory_test.py::TestMilvusMemory::test_get_relevant 
milvus_memory_test.py::TestMilvusMemory::test_get_stats 

============================== 5 passed in 21.75s ==============================

And I've also tested with the following instructions:

Name:  Summarize today's leading news
Role:  an AI designed to autonomously develop and run businesses with the
Goals: ["Visit a website which provides today's news.", 'Summarize the articles and write the results to text files', 'Terminate']
Continue (y/n): y
Using memory of type:  MilvusMemory
Using Browser:  chrome
 THOUGHTS:  I suggest browsing some news websites to get the latest headlines, then summarizing the articles and saving the results to a text file for later reference.

you can see it print "Using memory of type: MilvusMemory"

PR Quality Checklist

• My pull request is atomic and focuses on a single change.
• I have thoroughly tested my changes with multiple different prompts.
• I have considered potential risks and mitigations for my changes.
• I have documented my changes clearly and comprehensively.
• I have not snuck in any "extra" small tweaks changes

[wangxuqi]

This pull request may conflict with another one you have approved. If it does, I will fix it.

[richbeales]

Run flake8 autogpt/ tests/ --select E303,W293,W291,W292,E305,E231,E302
tests/milvus_memory_test.py:64:20: W292 no newline at end of file

[p-i-]

tests/milvus_memory_test.py:64:20: W292 no newline at end of file

Can you fix?