SAML/SLO: Return a response in logout endpoint

[tung2744]

ref DEV-2060

TODO:

• [x] Put the signature of the response to query if using redirect binding

[tung2744]

Updated, thanks!

[tung2744]

Fixed, thanks!

[tung2744]

I found that I forgot to remove the samlerror package, although no code is using them. I will remove them in next pr.