fix(amazonq): raise max @workspace indexing size to 4GB

[leigaol]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Description

1. The maximum allowed indexing sizes should not be 250MB. Tentatively setting it to 4GB.
2. Raise the default @workspace indexing size to 250MB.

Checklist

• My code follows the code style of this project
• I have added tests to cover my changes
• A short description of the change has been added to the CHANGELOG if the change is customer-facing in the IDE.
• I have added metrics for my changes (if required)

License

I confirm that my contribution is made under the terms of the Apache 2.0 license.