Add -skip-oidc-discovery option (#41)

* added karrieretutor go-oidc fork for using an AAD B2C Policy

* added karrieretutor go-oidc fork for using an AAD B2C Policy

* added --skip-oidc-discovery option

* added --skip-oidc-discovery option

* add simple test for skip-oidc-discovery option

* revert Dockerfile to pusher upstream

* revert Dockerfile to pusher upstream

* remove karrieretutor b2c option leftover

* remove karrieretutor b2c option leftover

* Fix typo (missing letters)

Co-Authored-By: marratj <marrat@marrat.de>

* Fix typo (missing letters)

Co-Authored-By: marratj <marrat@marrat.de>

* replace fake http client with NewProvider() from go-oidc

* remove OIDC UserInfo URL option (not required)

* add info about -skip-oidc-discovery to README

* add note to changelog

* Update outdated comment