Review and update of login auto initiation PR

For PR #3406

- Updated naming from 'redirect' to 'initate/initation'.
- Updated phpunit.xml and .env.example.complete files with the new
  option.
- Cleaned up controller logic a bit.
- Added content and design to the new initation view to not leave user
  on a blank view for a while.
- Added non-JS button to initiation view as fallback option for
  progression.
- Moved new test to it's own Test class and expanded with additional
  scenario tests for better functionality coverage.

app/Config/auth.php

@@ -13,10 +13,9 @@ return [
     // Options: standard, ldap, saml2, oidc
     'method' => env('AUTH_METHOD', 'standard'),
 
-    // Automatically redirect to external login provider if only one provider is being used
-    // instead of displaying a single-button login page and requiring users to click through
-    // Supported methods: saml2, oidc
-    'auto_redirect' => env('AUTH_AUTO_REDIRECT', false),
+    // Automatically initiate login via external auth system if it's the sole auth method.
+    // Works with saml2 or oidc auth methods.
+    'auto_initiate' => env('AUTH_AUTO_INITIATE', false),
 
     // Authentication Defaults
     // This option controls the default authentication "guard" and password