[REF] board: Move legacy files

This commit moves the content of the static board files to a dedicated
`legacy` folder to mark the transition with the new Owl environment.

Part-of: odoo/odoo#73311

addons/board/__manifest__.py

@@ -21,15 +21,14 @@ Allows users to create custom dashboard.
     'application': True,
     'assets': {
         'web.assets_backend': [
-            'board/static/src/scss/dashboard.scss',
-            'board/static/src/js/board_view.js',
-            'board/static/src/js/add_to_board_menu.js',
+            'board/static/src/**/*.scss',
+            'board/static/src/**/*.js',
         ],
         'web.qunit_suite_tests': [
             'board/static/tests/**/*',
         ],
         'web.assets_qweb': [
-            'board/static/src/xml/**/*',
+            'board/static/src/**/*.xml',
         ],
     },
     'license': 'LGPL-3',

addons/board/static/src/legacy/xml/board.xml

@@ -8,7 +8,7 @@
         <div class="oe_dashboard_links">
             <button type="button" class="button oe_dashboard_link_change_layout btn btn-secondary"
                 title="Change Layout..">
-                <img src="/board/static/src/img/layout_1-1-1.png" width="16" height="16" alt=""/>
+                <img src="/board/static/src/legacy/img/layout_1-1-1.png" width="16" height="16" alt=""/>
                 <span> Change Layout </span>
             </button>
         </div>
@@ -43,7 +43,7 @@
         </p>
         <ul>
             <li t-foreach="'1 1-1 1-1-1 1-2 2-1'.split(' ')" t-as="layout" t-att-data-layout="layout">
-                <img t-attf-src="/board/static/src/img/layout_#{layout}.png" alt=""/>
+                <img t-attf-src="/board/static/src/legacy/img/layout_#{layout}.png" alt=""/>
                 <i t-if="layout == currentLayout" class="oe_dashboard_selected_layout fa fa-check fa-lg text-success" aria-label='Layout' role="img" title="Layout"/>
             </li>
         </ul>