🪨 feat: add session token variable for AWS Bedrock

[philwilliammee]

Pull Request Template

Summary

This pull request adds a new environment variable BEDROCK_AWS_SESSION_TOKEN to the .env.example file.
This change enables session token-based authentication for AWS Bedrock, complementing the existing access key and secret key support.

Closes: #4895

Related Pull Requests

This PR is related to #4655, which introduces initial support for environment variables for AWS Bedrock. This PR complements it by adding the BEDROCK_AWS_SESSION_TOKEN variable for session token-based authentication.

Change Type

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

Testing

The changes were tested locally to ensure the .env.example file is updated correctly, with no syntax errors or issues when loaded into the application.

Test Configuration:

• No specific testing configuration is required as this is a static file update.

Checklist

• 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 (if applicable).
• I have made pertinent documentation changes.
• My changes do not introduce new warnings.
• Local unit tests pass with my changes.