[FIX] web: re-introduce on_change="0" to prevent onchanges for customization

In 10.0, adding on_change="0" allowed to prevent
default onchanges to occur for the field on which was added this attribute.

In 11.0, the rev. eaa66d1156
added a regression by removing this possibility.
It was an oversight, it was not an expected change
in the web client.

In 10.0, it's this line which bring this possibility:
https://github.com/odoo/odoo/commit/e8a00bc50da435d3859118ca127d20a2eb9a0cab#diff-ff0e90fb0eb4418a7f66e618e4b51323R444

opw-1883366

closes odoo/odoo#27952

addons/web/static/src/js/services/data_manager.js

@@ -273,7 +273,7 @@ return core.Class.extend({
             attrs.options = attrs.options ? pyeval.py_eval(attrs.options) : {};
         }
 
-        if (attrs.on_change && !field.onChange) {
+        if (attrs.on_change && attrs.on_change !== "0" && !field.onChange) {
             field.onChange = "1";
         }