Q: login fails if endpoint_url is set in [default] profile of ~/.aws/config

## Problem
Hi! Seemed to have figured out the issue and brining it to your attention!

The Error is in Amazon Q extension for vscode. Logging in with the free tier seems to use the default endpoint_url from the .aws config file if one is set, which results in an error opening the web view client, this seemed to be the most relevant general one:

`[error] webviewId="aws.amazonq.AmazonCommonAuth": Error: Webview error
-> Error: Webview backend command failed: "startCodeWhispererBuilderIdSetup()"
-> Error: Failed to connect to AWS Builder ID [FailedToConnect]
-> SyntaxError: Unexpected token '<', "

## Expected behavior
Opens the webview client to create builder ID
## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS: Windows
- Visual Studio Code version: newest
- AWS Toolkit version: newest
- Amazon Q version :newest

Start by reproducing Amazon Q free-tier login in VS Code with endpoint_url set in the default profile of ~/.aws/config, then compare it with the setting removed. Done means the Builder ID webview opens successfully without the reported connection and JSON parsing errors, with coverage for the described configuration.

Written by the indexing model from the issue text.