Entry to make needed documentation easier to discover and navigate in fewer clicks

Proposing an entry into docs that doesn't force developers to know the solution they are looking for, but guidesthem to the solution based on the problem they are solving. Ultimately it would answer questions like "Should I self host or use Azure AD?" This is a draft of what the flow might look like.

```mermaid
flowchart TD
A{What would you like to do?} -->|Add identity to my app| B
A --> |Learn about identity in ASP.NET Core| C
A --> |I'm new to identity. Where do I begin?| D
B{What identity solution are you considering?} --> |I don't know. Help me decide!| E
B --> |Self-hosted ASP.NET Core Identity| F
B --> |Self-hosted with a package like IdentityServer| G
B --> |Cloud-hosted Azure AD| H
B --> |Cloud-hosted Third-party| G
C[Auth in ASP.NET Core]
D[Identity introduction]
E[ASP.NET Core Identity Guidance]
F[Quickstart options]
G[Available identity solutions]
H[Azure AD and ASP.NET Core]
```

Epic: #29452