Feature request: support BigQuery WIF (Workload Identity Federation) in dbtcloud_profile

## Is your feature request related to a problem? Please describe.
Related to #705 — while that issue tracks WIF support for `dbtcloud_global_connection` (BigQuery), there's a parallel gap on the `dbtcloud_profile` resource. Today, environment-level profiles that should authenticate via WIF against a BigQuery WIF connection can't be fully managed/pinned as WIF profiles through `dbtcloud_profile` in Terraform. This makes it hard to manage the full WIF setup (connection + profile) end-to-end in Terraform without falling back to manual UI configuration for part of the setup.

## Describe the solution you'd like
Add support in the `dbtcloud_profile` resource (and/or its documentation) for explicitly creating and managing a WIF-authenticated BigQuery profile, consistent with how WIF is expected to work once #705 is resolved on the connection side.

## Describe alternatives you've considered
Currently, teams using BigQuery WIF need to configure the profile manually in the dbt Cloud UI and reference it in Terraform via `primary_profile_id` on `dbtcloud_environment` (supported since v1.8.0), rather than managing the profile itself as code.

## Additional context
Surfaced via a support investigation into BigQuery WIF profiles reverting to auto-generated, non-WIF profiles when `dbtcloud_environment.primary_profile_id` was left unset in Terraform — resolved for that case by explicitly setting `primary_profile_id`, but full profile management still isn't possible without this feature.