List Databricks accounts/workspaces grantable in access rules

Return the catalog of accounts/workspaces for the access-rule picker.

Defaults to onboarded workspaces. The raw account catalog is the whole Databricks account — 221 workspaces for pepsico against 95 we ingest from — so offering it by default listed workspaces nobody had onboarded (and BANNED ones) as grantable resources.