fix: respect vscode telemetry settings

Related issue: https://gitlab.com/gitlab-org/gitlab-vscode-extension/-/issues/980

This makes sure that our telemetry is never sent if user opted out according to guidelines in https://code.visualstudio.com/api/extension-guides/telemetry

We do not need to listen to configuration change events - it is just enough checking flag on each attempt we're trying to gather telemetry for sending data.