chore(cloud): remove EDB BigAnimal cloud deployment feature (#10018)

Removes the EDB BigAnimal cloud-deployment integration from the Cloud
Wizard. AWS RDS, Azure Database, and Google Cloud SQL remain as the
supported deployment targets. Covers the backend blueprint and pgacloud
provider, the frontend wizard steps/components/constants/icons, the
documentation page and screenshots, and stray BigAnimal references in
docstrings.

The BigAnimal-only "Cluster Type" wizard step is removed and the
remaining steps renumber from 0-5 to 0-4. As a side effect, the Azure
cluster-name availability check (previously dead code at activeStep == 2,
skipped past by the now-removed step) is now exercised. Two latent bugs
in that check are fixed at the same time: it inspected res.data.success
although checkClusternameAvailbility already resolves res.data, so a name
collision was never reported; and it passed an Error object to gettext(),
which cannot render it. It now uses res.success and surfaces
error.message with a readable fallback.

A 9.16 Housekeeping release-note entry is added documenting the removal.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>