Added required domains for push notifications

[cristianstoica]

googleapis.com subdomains are required for the push notifications to work

Proposed change

Type of change

• Document existing features within Home Assistant Companion App
• Document new or changing features for which there is an existing pull request elsewhere
• Spelling or grammatical corrections, or rewording for improved clarity
• Changes to the backend of this documentation
• Remove stale or deprecated documentation

Checklist

• I have read and followed the documentation guidelines.
• I have verified that my changes render correctly in the documentation.

Additional information

• This PR fixes or closes issue: Fixes #
• Link to relevant existing code or pull request:

[dshokouhi]

This should not be linked to an iOS footnote also the syntax may need to be adjusted as the build is failing. This may also be better fit on the networking troubleshooting page too: https://companion.home-assistant.io/docs/troubleshooting/networking