add sample client for extension grant without sub
add sample client for extension grant without sub

IdentityServer/IdentityServer4.Samples,IdentityServer/IdentityServer4.Samples,haoyk/IdentityServer4.Samples,haoyk/IdentityServer4.Samples,haoyk/IdentityServer4.Samples,IdentityServer/IdentityServer4.Samples,haoyk/IdentityServer4.Samples