MDL-69166 core_payment: Use a custom modal type for gateway selector

payment/templates/modal_gateways.mustache

@@ -0,0 +1,45 @@
+{{!
+    This file is part of Moodle - http://moodle.org/
+
+    Moodle is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Moodle is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+}}
+{{!
+    @template core_payment/modal_gateways
+
+    Moodle modal template with save and cancel buttons.
+
+    The purpose of this template is to render a modal.
+
+    Classes required for JS:
+    * none
+
+    Data attributes required for JS:
+    * none
+
+    Context variables required for this template:
+    * title A cleaned string (use clean_text()) to display.
+    * body HTML content for the boday
+
+    Example context (json):
+    {
+        "title": "Example gateways modal",
+        "body": "Some example content for the body"
+    }
+}}
+{{< core/modal }}
+    {{$footer}}
+        <button type="button" class="btn btn-primary" data-action="proceed">{{#str}} proceed {{/str}}</button>
+        <button type="button" class="btn btn-secondary" data-action="cancel">{{#str}} cancel {{/str}}</button>
+    {{/footer}}
+{{/ core/modal }}