Add Database

[StefanGreve]

Add a DBContext to the Backend using PostgreSQL and implement the following features

• Add a Light Novel Database (LNDB) (authenticated)
• Add a database for the Todo PowerShell moduele
• Add a database for my private book collection (public)
• Add a database for downloading files (e.g. PDFs)
• A organization database containing the following tables
  • User (for authentication purposes, see also issue Protect Requests with OAuth2.0 #2)

Things to Consider:

• database schemes?
• storage consideration for a file server?

Further Reading:

• https://learn.microsoft.com/en-us/ef/core/