Moves the `project_slugs` table to `entity_slugs` and `project_slugs_old` to `entity_slugs_old`. This is done to prepare for more entity types to be namespaced.

Note: the sequence migration has been tested:
1. Force migration revision to be `9058bf0a1a12` (before this).
2. Deploy with image tag `renku/renku-data-service:sha-345a1bb` (current `main`) and run `alembic check` and `alembic heads` to verify the DB is before this change.
3. Create some projects.
4. Re-deploy this PR and check that migration revision is `a11752a5afba` (after this).
5. Create more projects.

Introduce namespaced data connectors for Renku 2.0.

Details:
* Remove API routes for `/storages_v2`
* Add API routes for `/data_connectors`
* Add `data_connectors` table
* Drop the `storage_secrets` table
* Add `data_connectors_secrets` table

Fixes deleting storage configuration fields by setting them to `null`.

Adds authorization for data connectors in Renku 2.0.

Details:
* Authz changes to support data connectors

The `authz` schema changes include future support for linking data connectors to projects, but doing so is not implemented in this PR.

Adds the possibility to link a data connector to a project.

Details:
* Add API to link a data connector to a project
* Add API to list projects connected to a data connector
* Add API to list data connectors connected to a project

Note that `read` permissions are cascaded to direct members of the connected project.

* Creating a link from a private data connector to a project requires the `editor` role on both sides of the link.
* Creating a link from a public data connector to a project requires the `editor` role on the project.
* Removing a link requires either the `editor` role on the project or the `owner` role on the data connector.

Add support for saving and managing secrets for data connectors.

Details:
* Add API endpoints to list, update and delete saved secrets for a given data connector.

…nectors

# Conflicts:
#	components/renku_data_services/project/apispec.py

Fixes two issues with the migrations for data connectors:
1.  The migrations cannot be rolled back after creating a data connector. This was caused by leftover entries in the `entity_slugs` table.
2. The entity slug constraint was not created. The change was not picked up by Alembic; it seems Alembic can only handle `CheckConstraint` creation together with table creation, but not new constraints on an existing table, updates to them, or removing them from a table.

…nectors

# Conflicts:
#	components/renku_data_services/storage/api.spec.yaml
#	components/renku_data_services/storage/apispec.py
#	components/renku_data_services/storage/db.py
#	components/renku_data_services/storage/models.py

Add a background job to migrate "Data Sources" (`/storages_v2`) to "Data Connectors" (`/data_connectors`). Each storage item has a new data connector created and linked to the source project.

…nectors