Adding PackageSourceMapping while adding new sources

[enisn]

Description

Resolves https://github.com/volosoft/abp-studio/issues/2006

After this PR, when Nightly source is added to NuGet.Config file, also package mapping will be added.
Line:16 in the following image

Checklist

• I fully tested it as developer / designer and created unit / integration tests
• I documented it (or no need to document or I will create a separate documentation issue)

How to test?

• Remove all abp cli variations from dotnet global tools first:

dotnet tool uninstall -g volo.abp.Cli
dotnet tool uninstall -g volo.abp.studio.Cli

• Go to Volo.Abp.Cli folder and pack it and install it:

dotnet pack -c Release -o ./nupkg
dotnet tool update -g Volo.Abp.Cli --add-source ./nupkg --prerelease

• Then create a project and update it to nightly with command:

abp switch-to-nightly