confirmRegistration should return response rather than always true

[cjmeyer-polymorph]

Good day @furaiev, I was wondering if we could do the same as #261 but for confirmRegistration?
That is the function I need right now, but I imagine for others it would be good to also change verifyAttribute, changePassword, enableMfa, disableMfa, updateAttributes, deleteAttributes, and deleteUser in the same way since they all return true always.
Possibly setUserMfaPreference should also rethrow inside the catch, instead of returning false as it does now.

[furaiev]

hello @cjmeyer-polymorph ,
I'm wondering if it makes sense to catch, to do nothing and to rethrow.
It is actually the same behavior as we have right now - without catching.

It makes sense only if we catch and return false for example.

[cjmeyer-polymorph]

Sorry you're right, I didn't realise the error would bubble up and be able to be caught