Allow SQL backends to use a custom migrations table

[rmorlok]

Applications embedding go-workflows within their primary application may want to share the main application database with go-workflows. If they use go-migrate, today they will collide with the schema migrations table. Provide an option in go-workflows to specify which table should be used to avoid the conflict.

• Add WithMigrationsTable for the PostgreSQL and SQLite backends.
• Pass the configured table name through to golang-migrate so only migration bookkeeping changes; workflow state tables are unchanged.
• Cover the shared-database case where an embedding application already owns the default schema_migrations table.
• Document the new backend options.

Refs rmorlok/authproxy#539

[Copilot]

Pull request overview

This PR adds a configurable migrations bookkeeping table for the SQLite and PostgreSQL backends so applications sharing a database (and already using golang-migrate’s default schema_migrations) can avoid collisions while keeping go-workflows’ operational tables unchanged.

Changes:

• Add WithMigrationsTable(...) options for SQLite and PostgreSQL backends.
• Wire the configured table name into the golang-migrate driver config (sqlite.Config / postgres.Config).
• Add tests covering the shared-database scenario where schema_migrations is pre-owned by the embedding application, and update backend docs.

Show a summary per file

File	Description
docs/source/includes/_backends.md	Documents the new WithMigrationsTable backend option for SQLite/PostgreSQL.
backend/sqlite/sqlite.go	Passes configured migrations table into golang-migrate’s SQLite driver config.
backend/sqlite/sqlite_test.go	Adds a test verifying custom migrations table avoids touching existing schema_migrations.
backend/sqlite/options.go	Introduces MigrationsTable option and WithMigrationsTable setter for SQLite.
backend/postgres/postgres.go	Passes configured migrations table into golang-migrate’s Postgres driver config.
backend/postgres/postgres_test.go	Adds a test verifying custom migrations table avoids touching existing schema_migrations.
backend/postgres/options.go	Introduces MigrationsTable option and WithMigrationsTable setter for Postgres.

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• Files reviewed: 7/7 changed files
• Comments generated: 1

[rmorlok]

Sorry about that. My codebase didn't use MySQL so my agent must've missed that. Happy to push a fix if you want.

[rmorlok]

I pushed a change with the mysql support.

[rmorlok]

@cschleiden wondering if you had a chance to take a look at this PR 🙏