Inheritance to base DocType from a new app

Hi there,
I have almost 2 weeks since I’m facing with an issue, leave it beside, handling other tasks, but now for 2 days I’m looking for a solution and couldn’t find it, or I don’t know where to look.

I’m comming from odoo, and there when we wanted to add some more features (like new fields to a base doc type, when new app it was installed) to a base doctype, we simply use Inheritance, and magic.

Now, here, on a custom app I need a web form as an appointment, with some custom fields.
These new custom fields, are not all in the base Opportunity DocType, like uploading an image, and some more custom data fields.
My option to that was to create a new DocType in my app, and link the new Web Form, to this custom new DocType, and everything works like a charm, but I really need to connect this new Web Form, the the base Opportunity DocType and get the records there.

To do that, I could simply update the base Opportunity doctype, accordingly to my needs, BUT…
…and here is my issue. When I’ll install my app on a real server, how that will work, bcause I can’t update the base Opportunity doctype there too.
…so, am thinking if there is a way to use my custom app, in such way, that when I’m installing on a fresh production frappe-bench, to create automatically my custom fields in the base Opportunity DocType. Some kind on inheritance in odoo.

Can someone pls, pls pls, give an example on how can I do that, or show me something, or at least put me on the right path with some documentation, or a tutorial, anything to be able to see and learn to do it…???
Anything will be helpull
Thank you all in advance
Have a good day