open all `coder_app` in a new tab, not window

Version: [`v0.12.5+165b6fb`](https://github.com/coder/coder/commit/165b6fbc6a23fd5f58ed459ea50f42e642c2f696)

Open URL button in Port Forward now opens a new tab, not a new window

This is not consistent with IDEs opening, or was this change by design? `coder_app` `subdomains` open in new windows still.