feat(nuget): v3 to use Registrations endpoint instead of Search (#6943)

lib/datasource/nuget/__fixtures__/latestV2.json

lib/datasource/nuget/__fixtures__/nlog/nuspec.xml

lib/datasource/nuget/__fixtures__/nlog/v3_catalog_1.json

lib/datasource/nuget/__fixtures__/nlog/v3_catalog_2.json

lib/datasource/nuget/__fixtures__/nlog/v3_catalog_3.json

lib/datasource/nuget/__fixtures__/nlog/v3_registration.json

lib/datasource/nuget/__fixtures__/nunit/v2.xml

...source/nuget/__fixtures__/nunit/v2_noGitHubProjectUrl.xml

lib/datasource/nuget/__fixtures__/nunit/v2_no_release.xml

lib/datasource/nuget/__fixtures__/nunit/v2_paginated_1.xml

lib/datasource/nuget/__fixtures__/nunit/v2_paginated_2.xml

...asource/nuget/__fixtures__/nunit/v2_withoutProjectUrl.xml

lib/datasource/nuget/__fixtures__/nunit/v3_nuget_org.xml

lib/datasource/nuget/__fixtures__/nunit/v3_registration.json

lib/datasource/nuget/__fixtures__/nunitV2.json

lib/datasource/nuget/__fixtures__/nunitV3.json

...source/nuget/__fixtures__/nunitV3_noGitHubProjectUrl.json

lib/datasource/nuget/__fixtures__/nunitV3_privateFeed.json

...asource/nuget/__fixtures__/nunitV3_withoutProjectUrl.json

lib/datasource/nuget/__fixtures__/v3_index.json