Using plantuml (version 1.2024.4-3.2) in the TW container image (version
20241002.33.28) `plantuml` does not work out-of-the-box after installation:

After setting the JAVACMD variable (see 1231333), the attempt of rendering a
diagram causes the following error:

```
$ plantuml filename.puml 
Exception in thread "main" java.lang.RuntimeException: Fontconfig head is null,
check your fonts or fonts configuration
        at
java.desktop/sun.awt.FontConfiguration.getVersion(FontConfiguration.java:1263)
        at
java.desktop/sun.awt.FontConfiguration.readFontConfigFile(FontConfiguration.java:221)
        at
java.desktop/sun.awt.FontConfiguration.init(FontConfiguration.java:105)
        at
java.desktop/sun.awt.X11FontManager.createFontConfiguration(X11FontManager.java:696)
        at java.desktop/sun.font.SunFontManager$2.run(SunFontManager.java:352)
        at java.desktop/sun.font.SunFontManager$2.run(SunFontManager.java:309)
        at
java.base/java.security.AccessController.doPrivileged(AccessController.java:319)
        at java.desktop/sun.font.SunFontManager.<init>(SunFontManager.java:309)
        at java.desktop/sun.awt.FcFontManager.<init>(FcFontManager.java:35)
        at java.desktop/sun.awt.X11FontManager.<init>(X11FontManager.java:55)
        at
java.desktop/sun.font.PlatformFontInfo.createFontManager(PlatformFontInfo.java:37)
        at
java.desktop/sun.font.FontManagerFactory.getInstance(FontManagerFactory.java:51)
        at
java.desktop/sun.font.SunFontManager.getInstance(SunFontManager.java:242)
        at
java.desktop/sun.font.FontDesignMetrics.getMetrics(FontDesignMetrics.java:260)
        at
java.desktop/sun.java2d.SunGraphics2D.getFontMetrics(SunGraphics2D.java:870)
        at net.sourceforge.plantuml.Run.forceOpenJdkResourceLoad(Unknown
Source)
        at net.sourceforge.plantuml.Run.main(Unknown Source)
```

One has to manually install `fontconfig` to work around the issue.