bug: when using a generic webhook and url_fields (Query vars)

[Taaqif]

Describe the bug

I get this error when trying to use a generic webhook config

Please correct the errors in the form and try again.

edit "Argus" failed (invalid json)

failed to unmarshal service.Service:
cannot unmarshal array into Go struct field .Alias.notify.Base.url_fields of type string

To Reproduce
Steps to reproduce the behavior:
use this as a base,

notify:
    Apprise:
        type: generic
        url_fields:
            host: apprise
            path: notify/apprise
            port: "8000"
            query_vars: |
                { "$tag": "argus" }
        params:
            disabletls: "true"
            messagekey: body
            template: json

Create a webhook notify with this base, update query vars and try to save

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
To save correctly

[JosephKav]

Oh, looks like it was only converting stringifying notify fields when that notify was a default for the service.
(Also wasn't properly checking against notify/webhook defaults when creating the API payload).

Your example works now (thanks for that) and a few other variations I've tried (#712)