feat: mongo-db adaptor

[jobyid]

Added an adaptor which connects to mongo db atlas. Allowing you to store agent data in the cloud. If you have the appropriate tier you can also take advantage of their vector search functionality.
It should have all the same functionality as the other database adaptors.

Relates to:

Adding the option of using MongoDB in the cloud to store you agents data

Risks

Low, adds additional options for database usage

Background

What does this PR do?

Adds the option to store your agents data in MongoDB Atlas, and take advantage of their vector search. I have also updated the .env.example to include the additional variables for the mongo connection. And added to the agent index with functionality to initialise this database if required.

What kind of change is this?

Adding an additional feature

Why are we doing this? Any context or related work?

In my day job we exclusively use mongoDB for our database needs, for commercials and performance reasons. As we want to develop AI Agents, we need to have the mongoDB adaptor. IN the sprit of OpenSource I wanted to make sure it was available for the whole community to use as well.

Documentation changes needed?

A small additional input to the documentation is required to make users aware of the additional functionality and how it can be actioned.
Similar to the Postgres set up just adding in the appropriate connection string to the .env file will action he change to start using MongoDB as the database.

Testing

Where should a reviewer start?

The reviewer will need to have a least a free account with mongoDB atlas, then add the connection string and a Database name to the .env file. After that the agent should run as expected, saving memories as before. The reviewer can verify the saved data inside the MongoDB interface.

Detailed testing steps

1. Create MongoDB atlas account
2. Add connection string and Database name to .env file
3. Run agent
4. Verify inside MongoDB interface that the collections have formed and data is being stored