refactor(config): rewrite config parser

This PR refactors the configuration parser, replacing the old parser implementation with a new, more structured approach that includes validation and improved organization.

Key changes:
- Complete rewrite of the configuration parser using a map-based structure with built-in validation
- Addition of comprehensive validator functions for configuration values
- Renamed numerous configuration getter methods for better consistency

internal/template/functions.go

@@ -41,7 +41,7 @@ func (f *funcMap) Map() template.FuncMap {
 		"baseURL":          config.Opts.BaseURL,
 		"rootURL":          config.Opts.RootURL,
 		"disableLocalAuth": config.Opts.DisableLocalAuth,
-		"oidcProviderName": config.Opts.OIDCProviderName,
+		"oidcProviderName": config.Opts.OAuth2OIDCProviderName,
 		"hasOAuth2Provider": func(provider string) bool {
 			return config.Opts.OAuth2Provider() == provider
 		},