Resolve #3458178 "Add french IGN maps in 2.2 branch"

Add French IGN maps

src/Form/SettingsForm.php

@@ -107,6 +107,18 @@ class SettingsForm extends ConfigFormBase {
         ]),
     ];
 
+    $form['global_settings']['ign_api_key'] = [
+      '#type' => 'textfield',
+      '#size' => 43,
+      '#title' => $this->t('IGN API key'),
+      '#default_value' => $config->get('ign_api_key') ?? '',
+      '#description' => $this->t('If you use a <a href="@ign_maps" target="_ign_maps">IGN</a> map, please sign up for an account, <a href="@api_key" target="_api_key">create an API key</a> and paste it above. See <a href="https://geoservices.ign.fr/actualites/2023-11-20-acces-donnesnonlibres-gpf"> this article from IGN</a>',
+        [
+          '@ign_maps' => 'https://geoservices.ign.fr/',
+          '@api_key' => 'https://cartes.gouv.fr/',
+        ]),
+    ];
+
     $form['global_settings']['mapbox_access_token'] = [
       '#type' => 'textfield',
       '#size' => 83,
@@ -242,6 +254,7 @@ class SettingsForm extends ConfigFormBase {
 
     $this->config('leaflet_more_maps.settings')
       ->set('thunderforest_api_key', $form_state->getValue('thunderforest_api_key'))
+      ->set('ign_api_key', $form_state->getValue('ign_api_key'))
       ->set('mapbox_access_token', $form_state->getValue('mapbox_access_token'))
       ->set('mapycz_api_key', $form_state->getValue('mapycz_api_key'))
       ->set('here_api_key', $form_state->getValue('here_api_key'))