Implement EZP-22811: Prepare Symfony container configuration for multiple storage engines

This PR resolves issue https://jira.ez.no/browse/EZP-22811

> Having multiple storage engines available brings the need for generalized storage engine and storage engine database connection factories.

Extracted from https://github.com/ezsystems/ezpublish-kernel/pull/792.
Split from https://jira.ez.no/browse/EZP-22799 for easier review.

This adapts configuration for the situation where multiple storage engines exist.

`LegacyDbHandlerFactory` is removed for generalized `StorageConnectionFactory`. Database handlers are using connection service configured per storage and aliased to `StorageConnectionFactory` in compile time.
`StorageRepositoryProvider` is extracted from `StorageEngineFactory`, used by it and new `StorageConnectionFactory`.

### Additional

Some deprecated parameters and services in container configuration that were left over from https://github.com/ezsystems/ezpublish-kernel/issues/825 are removed here.

### TODOs

- [x] ~~write documentation~~