staging: Deploy blocking proxy on read-write storage instance

Blocking origin proxy is a storage patterned proxy. It's installable through yaml configuration in a storage rpc server.

Like the masking proxy, it requires a database to store the state.

Plan:

• Tag swh.storage v2.4.0
• swh/infra/ci-cd/swh-charts!391 (merged): Requires new storage version
• staging: Install database in postgresql cluster
• Initialize database model (manually without the toolbox)
• Add some blocked origins to the db
• swh/devel/swh-docs!430 (merged): swh-docs: Document access to the database
• swh/infra/ci-cd/swh-charts!393 (merged): swh-charts: Adapt storage read-write configuration to use it
• Checks

[1] hedgedoc draft: https://hedgedoc.softwareheritage.org/YQczK_9qR-qvNafFDm3q0g

Related to swh/devel/swh-storage!1124 (merged)