Invert the logic and disable "Expose via JSON:API" by default (Opt-in)

Problem/Motivation

Currently the README.md says

When installed the module activates resources for all of your enabled views, you can optionally disable the resource by editing the view.

Issues like

1. #3580102: Massive performance issues when having more than 100 Views
2. #3403820: /jsonapi/views endpoints not listed anywhere

show that this should better be inverted to be opt-in (and additionally maybe add a helper to do that in batch, e.g. on a settings page: #3575185: Add a settings page to disable resources in batch / drush.
Also I think it's safer to opt-in views that should provide JSON:API support to not publish any view unexpectedly, e.g. system views.

Steps to reproduce

Enable this module and have probably (unwanted) json:api endpoints for all views as documented

Proposed resolution

Enable the json:api endpoint only on views where needed

Remaining tasks

User interface changes

API changes

Data model changes