fix: Show proper error message when add token to existing account fails
requested to merge chez14/gitlab-vscode-extension:chez14/597-add-existing-account-shows-misleading-information-message into main
In this MR:
- Updated account_service.addAccount so that it throws exception when adding token for existing token.
- Updated test for related updated function.
Relates to #597 (closed)
Edited by Chris Qiang