Add support for dynamic config UI (#256)

* Add support for dynamic config UI

* Add support for section description

* Better dynamic class settings

Added dynamic_fields hash field - Stores all undeclared settings
[] method - Checks declared fields first, then falls back to dynamic hash
[]= method - Updates declared fields normally, stores others in hash
No runtime field declaration - Fields are never dynamically created on the class

* FIX proper lookup for provider keys

- Also validate configurable values properly.
- Change Provider factory to use Rails autoloading (Zeitwerk)

* Fix factory

The derive_adapter_name method relies on string manipulation ("PlaidAccount".sub(/Account$/, "") + "Adapter" → "PlaidAdapter"), but we already have explicit registration in place.

* Make updates atomic, field-aware, and handle blanks explicitly

* Small UX detail

* Add support for PlaidEU in UI also

- This looks like partial support atm

app/controllers/settings/providers_controller.rb

@@ -0,0 +1,108 @@
+class Settings::ProvidersController < ApplicationController
+  layout "settings"
+
+  guard_feature unless: -> { self_hosted? }
+
+  before_action :ensure_admin, only: [ :show, :update ]
+
+  def show
+    @breadcrumbs = [
+      [ "Home", root_path ],
+      [ "Bank Sync Providers", nil ]
+    ]
+
+    # Load all provider configurations
+    Provider::Factory.ensure_adapters_loaded
+    @provider_configurations = Provider::ConfigurationRegistry.all
+  end
+
+  def update
+    # Build index of valid configurable fields with their metadata
+    Provider::Factory.ensure_adapters_loaded
+    valid_fields = {}
+    Provider::ConfigurationRegistry.all.each do |config|
+      config.fields.each do |field|
+        valid_fields[field.setting_key.to_s] = field
+      end
+    end
+
+    updated_fields = []
+
+    # Perform all updates within a transaction for consistency
+    Setting.transaction do
+      provider_params.each do |param_key, param_value|
+        # Only process keys that exist in the configuration registry
+        field = valid_fields[param_key.to_s]
+        next unless field
+
+        # Clean the value and convert blank/empty strings to nil
+        value = param_value.to_s.strip
+        value = nil if value.empty?
+
+        # For secret fields only, skip placeholder values to prevent accidental overwrite
+        if field.secret && value == "********"
+          next
+        end
+
+        # Set the value using dynamic hash-style access
+        Setting[field.setting_key] = value
+        updated_fields << param_key
+      end
+    end
+
+    if updated_fields.any?
+      # Reload provider configurations if needed
+      reload_provider_configs(updated_fields)
+
+      redirect_to settings_providers_path, notice: "Provider settings updated successfully"
+    else
+      redirect_to settings_providers_path, notice: "No changes were made"
+    end
+  rescue => error
+    Rails.logger.error("Failed to update provider settings: #{error.message}")
+    flash.now[:alert] = "Failed to update provider settings: #{error.message}"
+    render :show, status: :unprocessable_entity
+  end
+
+  private
+    def provider_params
+      # Dynamically permit all provider configuration fields
+      Provider::Factory.ensure_adapters_loaded
+      permitted_fields = []
+
+      Provider::ConfigurationRegistry.all.each do |config|
+        config.fields.each do |field|
+          permitted_fields << field.setting_key
+        end
+      end
+
+      params.require(:setting).permit(*permitted_fields)
+    end
+
+    def ensure_admin
+      redirect_to settings_providers_path, alert: "Not authorized" unless Current.user.admin?
+    end
+
+    # Reload provider configurations after settings update
+    def reload_provider_configs(updated_fields)
+      # Build a set of provider keys that had fields updated
+      updated_provider_keys = Set.new
+
+      # Look up the provider key directly from the configuration registry
+      updated_fields.each do |field_key|
+        Provider::ConfigurationRegistry.all.each do |config|
+          field = config.fields.find { |f| f.setting_key.to_s == field_key.to_s }
+          if field
+            updated_provider_keys.add(field.provider_key)
+            break
+          end
+        end
+      end
+
+      # Reload configuration for each updated provider
+      updated_provider_keys.each do |provider_key|
+        adapter_class = Provider::ConfigurationRegistry.get_adapter_class(provider_key)
+        adapter_class&.reload_configuration
+      end
+    end
+end