Consider implementing an ignore file/setting

[TomasHubelbauer]

I have a repository which has a data directory in it. This data directoty is Git-ignored and in its tree has several .NET Core projects for various reasons. I would like to prevent the C# extension from prompting me to install dependencies for these nested .NET Core projects each time I open the main project with the data directory in it. The extension's contributions have some settings for supressing certain warnings and such, but I would like this to only apply to the data directory and have the extension work as usual for the root project. Is this something you're open to including in the extension? My idea is that either a .netignore file could exist that would work identically to the .gitignore file or there could be a repository-level (the .vscode directory) setting where I could ignore it using a glob pattern.

[DustinCampbell]

Thanks for filing this issue! I believe it's a duplicate of #1694 and OmniSharp/omnisharp-roslyn#896.

Let me know if you disagree.