feat(nuget): allow detecting source URLs via package contents (#28071)

docs/usage/self-hosted-experimental.md

...tasource/nuget/__fixtures__/nlog/NLog.4.7.3-no-repo.nupkg

...dules/datasource/nuget/__fixtures__/nlog/NLog.4.7.3.nupkg

lib/modules/datasource/nuget/common.ts

lib/modules/datasource/nuget/index.spec.ts

lib/modules/datasource/nuget/types.ts

lib/modules/datasource/nuget/v3.ts