Add dotnet docs <symbol> for quick API lookup

### Add dotnet docs for quick API lookup
Add a new CLI command:
dotnet docs

This allows devs to quickly look up .NET API documentation directly from the terminal, similar to go doc.

### Describe the solution you'd like

A simple CLI tool that uses provides documentation of a symbol. I think either using getting it from Roslyn or microsoft learn. Roslyn for quick offline documentation, or from Microsoft.Learn and cache it for repeated information.

The goal is to have fast, local-first API documentation lookup. And provide it with sdk in which that information would be helpful. Can work without internet by using Roslyn, and have it naturally integrated with dotnet cli so you have the functionality directly with the sdk, which will be convinent for terminal users.

The goal is not to replace full documentation, not to provide tutorials, and not to be a complex search engine functionality.

### Additional context
Input example

```
dotnet docs string.Join
dotnet docs List
dotnet docs HttpClient.SendAsync
```

Output example

```
System.String.Join

Joins elements of an array into a single string.

Overloads:
- Join(string separator, string[] values)
- Join(char separator, string[] values)

Parameters:
separator: The string to use as a separator.
values: The array of strings.
```

Optional features:
--open -> open learn page in browser
--web -> fetch richer documentation
Fuzzy search (dotnet docs join)
project aware resolution - respecting referenced assemblies

### Willingness to Contribute

I have tried finding issues that I could contribute to, and I believe this is something that I could contribute.
I believe this would significantly improve the cli experience for dotnet developers by making API discovery fast, local and accessible without leaving the terminal or IDE (embedded terminal)