grids random payload defined

ok so next step is go on the server side
- extract recipient, amount, payload,
- register search pattern
- wait for matching transaction to appear
- notify correct party

priv/static/js/dist/grids-basic.js

@@ -20,6 +20,10 @@ async function main() {
     let submit_btn = document.getElementById('grids-submit');
     let grids_url_elt = document.getElementById('grids-url');
     let grids_png_elt = document.getElementById('grids-png');
+    let rand_data = new Uint8Array(32);
+    window.crypto.getRandomValues(rand_data);
+    let hex = rand_data.toHex().toUpperCase();
+    p_input.value = 'text payload ' + hex;
     // Page initialization
     submit_btn.addEventListener('click', async function (e) {
         await on_submit(n_input, r_input, a_input, p_input, grids_url_elt, grids_png_elt);