Support GitHub Apps Installation authentication

This PR introduces two things:

A new CLI for the SDK that allows users to authenticate using GitHub Apps Installation tokens. The CLI is a simple command-line tool that allows users to authenticate with GitHub using a GitHub App Installation token or a personal access token. The CLI is designed to be easy to use and can be run from the command line on any platform. It's primary use case is for tight loop development validation and testing.
New classes for app installation and personal access token authentication. These classes are currently used in the CLI for authentication and are for general purpose authenticate with GitHub using GitHub Apps Installation tokens or personal access tokens.

Added the new CLI project to the solution.
Added a new entry point for the CLI that accepts arguments for different authentication methods.
Created a new project file for the CLI.
Added a README to explain how to use the CLI and set up environment variables for authentication.
Added a step to build the main project before the CLI, as the CLI references the main project locally.

Added new classes for app installation and personal access token authentication.
Added new classes to provide authentication for the CLI.

Test coverage has been added to ensure that the new classes and methods are working as expected.

Coverage: 83% | Branch coverage: 72%
dotnet test -p:CollectCoverage=true -p:CoverletOutput=TestResults/ -p:CoverletOutputFormat=opencover -p:ExcludeByFile="**/GitHub/**/*.cs"

Screenshot 2024-06-04 at 9 45 15 AM

[x] Tests for the changes have been added (for bug fixes / features)
[x] Docs have been reviewed and added / updated if needed (for bug fixes / features)

Please see our docs on breaking changes to help!

octokit / dotnet-sdk