Google provider: support universe_domain via connection extras

[shahar1]

Body

The current Google provider universe-domain support relies on the process-wide environment variable GOOGLE_CLOUD_UNIVERSE_DOMAIN (introduced in #66159).

That is constraining for real deployments:

• A single Airflow deployment cannot target multiple universes at once.
• The configuration is not visible/discoverable in the Airflow connection UI.

This issue tracks follow-up work to support universe domain configuration through Google connection extras (with a compatibility path for existing env-var usage).

Related review comment:

• Add universe_domain support for GoogleBaseHook #66159 (comment)

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Drafted-by: GitHub Copilot (GPT-5.3-Codex)

[shahar1]

CC: @VladaZakharova @MaksYermak