Adds a '--use-memory' flag to choose memory backend at runtime

[sadmuphin]

Background

To easily switch between memory backends without the need to edit the .env file

Changes

Adds a --use-memory argument so the user can choose a supported memory backend when running the script

Documentation

I have specified some comments in the memory/__init__.py file

Test plan

Not thoroughly tested, but should work out of the box (hopefully)

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

[adamnmcc]

this is available in the env file as MEMORY_BACKEND=local

[luiscosio]

This should include a modification to the README since it's not documented the use of the environment variable @adamnmcc

[sadmuphin]

This PR is primarily supposed to be a QOL update, it's not a replacement for any environment variables.

@luiscosio Correct, and it's not included in the template file, I've added these in #971

[sadmuphin]

Just as a heads up if this does get merged (or any maintainers want to merge it) #852, #424 and any other memory backend providers will have to add this code on successful module importation (in memory/__init__.py):

supported_memory.append('<backend>')

[nponeccop]

It's not about if, it's about when. It will get merged in the Batch 3.