Consume snippet generator as a tool (#22783)

* Update eng\scripts\Update-Snippets.ps1 to consume Snippet Generator tools package from azure-sdk-tools DevOps feed

Remove eng\snippetgenerator

Update Update-Snippets.ps1 to consuem Snippet Generator tyools package from azure-sdk-tools DevOps feed

* Remove reference to DevOps feed in NuGet.Config, add feed link directly as source in Update-Snippets.ps1

* Switch to using azure-sdk-for-net devOps feed

* Refactor Update-Snippets for Linux Agents

* Run snippet generator in a new process

* Install SnippetGenerator tools as a seperate pipeline step

Author: chidozieononiwu