DEV: Prepare new structure for migrations-tooling (#26631)

* Moves existing files around. All essential scripts are in `migrations/bin`, and non-essential scripts like benchmarks are in `migrations/scripts`
* Dependabot configuration for migrations-tooling (disabled for now)
* Updates test configuration for migrations-tooling
* Shorter configuration for intermediate DB for now. We will add the rest table by table.
* Adds a couple of benchmark scripts
* RSpec setup especially for migrations-tooling and the first tests
* Adds sorting/formatting to the `generate_schema` script

migrations/db/schema/001-schema_migrations.sql

@@ -0,0 +1,6 @@
+CREATE TABLE schema_migrations
+(
+    path       TEXT     NOT NULL PRIMARY KEY,
+    created_at DATETIME NOT NULL,
+    sql_hash   TEXT     NOT NULL
+);