Make it easier to debug SAML errors

Recently I had to debug SSO errors where users were seeing 500 errors because of some infra configuration errors, but debugging this was very difficult as I had to figure out and spend some time to get some logging setup.

The way I did was to add [logging into X-ray](https://github.com/humanmade/aws-xray/) with more details for the error from `$saml->getLastErrorReason()` and `$saml->getLastErrorException()`

https://github.com/humanmade/wp-simple-saml/blob/236a41b0dc3286b434313bd8a4766f9959ec10c1/inc/namespace.php#L315-L337

I am thinking about how we can make it easier to debug this, One of the simplest solutions I am thinking of is to also trigger WordPress actions with related information and let the application code handle different logging?