Add existence check to prevent errors accessing the clipboard in insecure contexts

[sentry-io]

If accessed outside of a secure context, the navigator.clipboard property may be undefined, we should add a guard to handle this case: https://developer.mozilla.org/en-US/docs/Web/Security/Secure_Contexts

Sentry Issue: STUDIO-FCB

TypeError: navigator.clipboard is undefined
  at copyToken (/static/studio/channel_list-a4b1d721c0ab188c1538.js:2:1355598)
  at click:append (/static/studio/channel_list-a4b1d721c0ab188c1538.js:2:1354962)
  at invokeWithErrorHandling (/static/studio/channel_list-a4b1d721c0ab188c1538.js:2:737343)
  at invoker (/static/studio/channel_list-a4b1d721c0ab188c1538.js:2:739953)
  at invokeWithErrorHandling (/static/studio/channel_list-a4b1d721c0ab188c1538.js:2:737343)
...
(5 additional frame(s) were not displayed)

[marcellamaki]

Fixed with #3698