Add functionality to configure NetBeans snap

### Description

**NetBeans 19** delivered as a [snap](https://snapcraft.io/netbeans) has no way to be configured. For example, to set the minimum Java heap size requires a modification of the configuration file:

`/snap/netbeans/current/netbeans/etc/netbeans.conf`

When opening the file, we see that it is **unwritable**:

If trying to [configure it as a snap](https://snapcraft.io/docs/configuration-in-snaps), we see that there are no configuration options:

```
$ sudo snap get netbeans
error: snap "netbeans" has no configuration
```
Please add functionality to configure the NetBeans snap.

### Use case/motivation

_No response_

### Related issues

Related comments: [link1](https://github.com/apache/netbeans/discussions/5614#discussioncomment-5245196), [link2](https://github.com/apache/netbeans/issues/6423#issuecomment-1719518711)

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

No

The issue names no repository files or tests; start by reading the Snap configuration documentation and inspecting /snap/netbeans/current/netbeans/etc/netbeans.conf to understand the current package boundary. Done means NetBeans snap options can be exposed and changed through snap configuration, including the Java heap setting described in the issue.

Written by the indexing model from the issue text.