Supporting extra CCloud auth callback URI schemes

[shouples]

Background

We delegate our CCloud authentication handling to the sidecar, and it's currently only using the vscode:// URI scheme (config here) in its callback templates. This means anyone using the extension outside of VS Code itself will not be able to use the CCloud sign-in feature, even if other features work out of the box.

Proposal

We could add specific links/buttons in the sidecar templates that allow users to choose which callback URI scheme should be used based on the application they're working with:

• vscode:// for normal VS Code
• vscode-insiders:// for VS Code Insiders (ref)
• code-oss:// for Code - OSS / VS Codium
• cursor:// for Cursor (https://forum.confluent.io/t/cursor-support-for-vscode-confluent-cloud-integration/12500/2)

...more?

The extension could also send the sidecar the env.uriScheme to inform which URI scheme to use.