[BC brake] Avoid DB for configuration

[RoSk0]

Coming from aacotroneo/laravel-saml2 I discovered multiple issues in this package:

• no IDP key rollover support - Thoughts on Multiple IDP certificates support? #21
• IDP configuration is stored in the DB making it more error-prone to manage a single configuration with
  only environment specific details changing and overall being not cloud native friendly
• IDP machine name replace by the UUID Possible to use idpName instead of uuid? #66
• single log out require custom coding - not much , but why in the first place? How to handle logouts when Idp notifies you #105

I believe storing IDP configuration in the DB complicates a lot of things and most importantly makes it harder to maintain this project.

I've tried to consider reasons behind that move but couldn't find any. So now I'm proposing revert back to the v1 approach and get rid of the DB as the configuration storage.

Targeting master to simplify review, but significance of the change definitely warrant a new major version release. I know there was a start on v3 in #88 , but still believe the project and it's users would benefit from the simplicity and additional features that this change brings:

• all configuration in one place
• simplified configuration management utilizing environment
• support off all features of the SAML PHP Toolkit

[breart]

Hey @RoSk0, thank you for this PR. Valid issue observations and some of them definitely need to be addressed.

This forked solution has been developed in 24Slides as a result of the business needs we had, and we decided to open-source it so other people that share the same problem could use it.

The reasons behind the decision to store IdP configurations in the database were the following:

1. We had over 10 different IdPs we worked with and that number was projected to increase to 50 or even 100. It made us realize keeping all those configurations in some kind of configuration files would result in higher maintenance cost
2. Strategically, we wanted in the future to make it possible for customers to manage their IdP configuration right from their account settings page. Database would be the obvious choice here.

I hope it gives you needed context. This PR won't be merged due to the arguments stated above, but feel free to create a fork for simpler cases like yours.