Implement custom identity query

[MarkusThielker]

Description

Right now, querying for an identity using the identifier is using Kratos' List Identities endpoint with the experimental preview_credentials_identifier_similar query param. This endpoint doesn't provide the search features I would want for searching an identity.

It basically matches using a startsWith(<query>) instead of an === query.

This is why I will implement a custom query function by directly connecting to the Kratos DB using Drizzle ORM. With that I can query on identitfiers, credentials, traits and more and provide a reliable query to find an identity.

The query will have to be tested on big datasets to make sure it is fast and also doesn't slow down Kratos.