Expose `PUBLISHABLE_KEY` in `supabase branches get`

[PaintingWithCode]

Existing issues

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Affected area

Other

Problem to solve

The CLI currently only returns the legacy ANON_KEY in the branch get response, and having migrated to the new API key format we're unable to get the default PUBLISHABLE_KEY for a branch from the CLI in order to inject it into our preview app's environment variables.

Proposed solution

Similar to the new secret key being returned in SUPABASE_DEFAULT_KEY, add a new field for SUPABASE_PUBLISHABLE_KEY in the response for supabase branches get.

Alternatives considered

No response

Additional context

No response