Add ReadOnlyMode to NuGetGallery.csdef.
Add ReadOnlyMode to NuGetGallery.csdef.

mtian/SiteExtensionGallery,KuduApps/NuGetGallery,ScottShingler/NuGetGallery,grenade/NuGetGallery_download-count-patch,projectkudu/SiteExtensionGallery,skbkontur/NuGetGallery,projectkudu/SiteExtensionGallery,mtian/SiteExtensionGallery,JetBrains/ReSharperGallery,grenade/NuGetGallery_download-count-patch,KuduApps/NuGetGallery,grenade/NuGetGallery_download-count-patch,JetBrains/ReSharperGallery,ScottShingler/NuGetGallery,KuduApps/NuGetGallery,skbkontur/NuGetGallery,mtian/SiteExtensionGallery,KuduApps/NuGetGallery,KuduApps/NuGetGallery,projectkudu/SiteExtensionGallery,skbkontur/NuGetGallery,JetBrains/ReSharperGallery,ScottShingler/NuGetGallery