[FIX] web: make AutoComplete's value optional

The recent use of owl AutoComplete component in the website builder
broke some things (see [1]). This commit handles this bug:

Steps to reproduce:
- Go to /web?debug=1
- Go to the website app
- Enter edit mode
- Drop the text-image snippet
=> Traceback

This was because the AutoCompleteWithPages extension of website was
inheriting the AutoComplete props whose "value" prop was not optional
but was not used for this case.

This commit goes the easy way: make the original prop optional with the
default value being the empty string.

[1]: https://github.com/odoo/odoo/commit/86a9171ec7790aa09f2b9a50dcb26deb029e8bed

closes odoo/odoo#141751

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/web/static/src/core/autocomplete/autocomplete.js

@@ -371,7 +371,7 @@ export class AutoComplete extends Component {
 Object.assign(AutoComplete, {
     template: "web.AutoComplete",
     props: {
-        value: { type: String },
+        value: { type: String, optional: true },
         id: { type: String, optional: true },
         onSelect: { type: Function },
         sources: {
@@ -398,6 +398,7 @@ Object.assign(AutoComplete, {
         class: { type: String, optional: true },
     },
     defaultProps: {
+        value: "",
         placeholder: "",
         autoSelect: false,
         dropdown: true,