Chore: removes props mutation (#2056)

While investigating some potential mutations
[here](https://ops.grafana-ops.net/d/83f4951f-2ef3-4260-91a0-39a031992b75/getmutationobserverproxy-logs)
I was able to find these mutating
[lines](https://github.com/grafana/grafana-zabbix/blob/main/src/datasource/components/ConfigEditor.tsx#L55-L57)

Although this works right now, this might not work in future Grafana
versions. This PR makes sure we don't mutate the props.

I haven't been able to test this manually so I could use some help to
make sure the plugin works as expected.

---------

Co-authored-by: ivanahuckova <ivana.huckova@gmail.com>

src/test-setup/jest-setup.js

@@ -1,4 +1,7 @@
 import { PanelCtrl, MetricsPanelCtrl } from './panelStub';
+import { TextEncoder, TextDecoder } from 'util';
+
+Object.assign(global, { TextDecoder, TextEncoder });
 
 jest.mock(
   'grafana/app/features/templating/template_srv',