Configurable Project Files in Projects view

### Description

Many Java projects have some other configuration files which are not visible in the Projects view. Users have to switch to the Files view to see or edit these files. Examples of these files are Spotbugs, PMD, .gitignore, README.md, pipeline configurations (.gitlab-ci.yaml), and Kubernetes/helm configurations. It would be nice to have a configuration for the Project Files node that allows users to select which files are visible there.

There is a plugin Show Ignored Files https://github.com/Chris2011/ShowIgnoredFiles that adds a new node Ignored Files & Folders into the Projects view and a user can configure what he wants to see there
I believe that it would help many users to find a edit their project files and this functionality should be provided out of the box.

### Use case/motivation

Currently, users have to switch to Files which is not good UX. Users can use `Ctrl` + `Shift` + `2` to switch to the Files view but it is annoying because of the switch between views.

### Related issues

There is a discussion https://github.com/apache/netbeans/discussions/6387

### Are you willing to submit a pull request?

No

Start with the NetBeans Projects view and Files view entry points, then read the related discussion in #6387 and compare the Show Ignored Files plugin. Done means users can configure which project files appear under the Project Files node without switching views.

Written by the indexing model from the issue text.