Add support for multiple database providers

[MeikelLP]

The following adjustments were made:

• Added support for Postgresql and Sqlite additionally to the already existing Mysql support
• Replace FluentMigrator with EntityFrameworkCore because it's more known in the professional and hobbyist .NET world. FluentMigrator is more or less legacy
• Cleanup dependencies between Auth & Game app. Originally the game app would access the auth database to validate some things (delete code is saved in the account). Now the game app talks to the auth app via a dedicated API
• The above stated API is implemented via HTTP (AspNetCore minimal API). This will require some security setup in the future but works fine for now. This wont be hard as this is a very common task in web / asp.
  • Maybe we can add some more basic APIs here (like account creation) and maybe some more native http support for plugins like the prometheus exporter plugin
• Replaced raw sql statements with EFCore ORM / LINQ style queries. This should be okay for now. We maybe will need to use dapper again some day but EF Core is quite performant nowadays and we will also leverage caching so there is not reason to write multiple queries (for every provider each)
• The migrator app was removed. The auth & game app will now check for db migrations on startup and apply them accordingly.
• Added tests to spin up a db and migrate it from zero to the latest to always check for at least some level of stability for our migrations
• Changed settings: No more Host, Port, User, Password. Only Provider and ConnectionString which is much more powerful in combination. Help for connection strings can be found here
• This change is destructive as I do not care about any previous databases. I assume this will be the new initial migration for simplicity

Dependency changes:

• Removed Dapper
• Removed FluentMigrator
• Added EFCore

TODOs

• [x] Implement multiple db providers
• [x] Fix tests
• [x] Adjust CI
• [x] Update docs

[sonarcloud[bot]]

Quality Gate failed

Failed conditions
2 Security Hotspots
30.6% Duplication on New Code (required ≤ 3%)
E Security Rating on New Code (required ≥ A)
D Reliability Rating on New Code (required ≥ A)

See analysis details on SonarCloud

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