Introduce SEND_USERNAME_TO_MODEL to send username instead of id to model calls

[alihacks]

Summary

Some users may benefit from logging username instead of user id when calling LLMs, this change introduces environment variable SEND_USERNAME_TO_MODEL which when set to true will send username instead of id.

Change Type

Please delete any irrelevant options.

• New feature (non-breaking change which adds functionality)

Testing

Tested with Azure Open AI and confirmed username can be passed when this variable is set

Checklist

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• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• I have made pertinent documentation changes
• My changes do not introduce new warnings
• Local unit tests pass with my changes
• A pull request for updating the documentation has been submitted.

[alihacks]

Sorry -I have been away last week. Doc updates are ready at LibreChat-AI/librechat.ai#149

[owengo]

Hello, there is an issue with this patch with Anthropic: the user sent to the api at api/app/clients/Anthropic/Client.js should be non identifiable as per:
https://docs.anthropic.com/en/api/messages

If the api detects it's an email address or other non-anymous data the request is blocked with a 400 error.

Cline suggests this quick fix:

    const metadata = {
      user_id: process.env.SEND_USERNAME_TO_MODEL === 'true'
        ? crypto.createHash('sha256').update(this.user).digest('hex')
        : this.user,
    };

It seems there is also an issue with the subsequent calls to "spendToken"