Added BaGet Windows service and upgraded to .Net 6.0

[pieroviano]

Summary of the changes:

• Added BaGet Windows service
• Introduced automatic package generation at build
• Added MSI setup project for Windows service
• Upgraded to .Net 6.0 and .Net 7.0
• Upgraded package references

[mlockett42]

@loic-sharma Azure Web Apps no longer support .Net Core 3.1 so the fact that this project is stuck on this version is preventing us from updating your infrastructure right now. Please give this PR your attention ASAP

[mdarocha]

From what I've attempted to build this PR, it errors out. Do you have any pointers?

• Running dotnet publish src/BaGet -p:TargetFramework=net7.0 --configuration Release --output out/ errors out with an error of TransformWebConfig

• Running dotnet publish src/BaGet -p:TargetFramework=net7.0 -p:IsTransformWebConfigDisabled=true --configuration Release --output out/ passes, but the out folder is not created and no output is made.

I'm trying to build it using .NET 7.0 on Linux