[Runtime] Reduce dependency to speed up CI and reduce image size

[xingyaoww]

What is the problem that this fixes or functionality that this introduces? Does it fix any open issues?

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Give a summary of what the PR does, explaining any non-trivial design decisions

• Reduce dependency installed for runtime (only main and runtime) to speed up CI and reduce image size
• Make llama-index an optional dependency (so we don't need to install torch). LongTermMemory is the only one class that depends on it, but it is not currently used anywhere in OpenDevin.
• Make LongTermMemory optional and prompt user to manually install poetry install --with llama-index when it is needed.

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Other references

[xingyaoww]

(good, all CI passed!)

[neubig]

Faster CI 🤤