feat(persistence): Allow using custom database schema for persistence. Fixes #2452

[jnt0r]

Fixes #2452

Motivation

Currently, Argo Workflows uses the default database schema for persistence. This PR introduces the ability to configure a custom schema. As MySQL does not have the concept of schemas and used the database name as kind of a schema, it is only introduced to postgres.

Key benefits:

• Namespace Isolation: Clearly separate Argo Workflows metadata from other tables in the same database.
• Permissions Management: Allows DBAs to restrict the Argo service user to a specific schema.
• Flexibility: Supports complex infrastructure setups where the default schema (e.g., public in PostgreSQL) is restricted or reserved for other purposes.

Modifications

• It is now possible to set the optional "schema" Property in the persistence config for the workflow controller (configmap).
• The schema is created for postgresql if the schema is set and does not already exist (migration)

Verification

I adjusted the Unit Tests to verify the schema is set to the database connections only when schema is explicitly set. When the schema is not overridden the default schema is used to provide downward compatibility.

Locally tested with hack/db (setting custom dsn like it would be generated in code: -d postgres://postgres:password@host.docker.internal:5432/postgres?search_path=argo)

Also, I created a new integration test with postgres and mysql testcontainers to test the connection is correctly using the new schema.

Should I also create a new E2E test?

Documentation

Added the schema property in examples and added additional chapter to "workflow archive" chapter.

[tico24]

Each sentence on a new line please. It make future reviews easier. Thanks!