RG config client — CRUD, models and versioned generate methods

[carlosfunk]

Adds client support for DataMasque ruleset-generation configs: server-side masks-per-label configs consumed by the versioned generate APIs.

Commits

• feat(client): add RG config CRUD and versioned generate methods

What's in it

• RGConfig pydantic model + RGConfigClient mixin: list/get/create/update/delete + get_default_rg_config_yaml() against rg/configs/
• Versioned generate methods mirroring the discovery *_from_config split: generate_ruleset_with_rg_config (v3), generate_file_ruleset_with_rg_config (v2), start_async_ruleset_generation_with_rg_config (v2), start_async_ruleset_generation_from_csv_with_rg_config (v2). Old methods keep the old endpoints (server default RG config).
• Old generate request models reject rg_config and point callers at the new methods.
• CSV/multipart note: rg_config=None is sent as an empty form field; DRF coerces '' to null on relational fields (verified end-to-end against a live server).

[cph-datamasque]

Mostly minor issues.

Do we want a RGConfigNotFoundError exception type to mirror the handling of 400 responses for other APIs?

Another thing that needs to be done at some point: the docs are out of date and need regenerating. Up to you if you want to do that in this MR, or we could raise a ticket to do it another day.

[carlosfunk]

Do we want a RGConfigNotFoundError exception type to mirror the handling of 400 responses for other APIs?

Added.

Another thing that needs to be done at some point: the docs are out of date and need regenerating. Up to you if you want to do that in this MR, or we could raise a ticket to do it another day.

Added the two stubs for this PR.

[cph-datamasque]

Approved after one wording change