Allow login through OpenID Connect (#16221)

* added OpenID Connect as an SSO option

* minor fixes

* added comments, removed an option that shouldn't be set

* fixed Gemfile.lock

* added newline to end of Gemfile.lock

* removed tab from Gemfile.lock

* remove chomp

* codeclimate changes and small name change to make function's purpose clearer

* codeclimate fix

* added SSO buttons to /about page

* minor refactor

* minor style change

* removed spurious change

* removed unecessary conditional from ensure_valid_username and added support for auth.info.name in user_params_from_auth

* minor changes