Add an option to set-up font cache folder

[masesdevelopers]

Is your feature request related to a problem? Please describe.
Currently NetPDF use the default location for font cache, it is needed a new option to override the default value

Describe the solution you'd like
Following what was written in https://stackoverflow.com/questions/41304855/pdfbox-disable-font-cache-or-change-its-location add a new configuration property to override the default value

Describe alternatives you've considered
Use a command line option

Additional context
N/A

[masesdevelopers]

Currently

NetPDF/.github/workflows/generateclasses.yaml

Line 157 in cabcc9e

run: jnetreflector -TraceLevel 1 -TraceTo %GITHUB_WORKSPACE%\JNetReflector.txt -OriginRootPath %GITHUB_WORKSPACE%\jars -DestinationRootPath %GITHUB_WORKSPACE%\src\ -ConfigurationFile %GITHUB_WORKSPACE%\src\configuration.json

is not able to use the font cache parameter, maybe it is important that JNetReflector can accept JVM options in the JSON configuration file.

[masesdevelopers]

Issue masesgroup/JNet#594 is closed, try to update configuration and test its behavior

[masesdevelopers]

Adding the following snippet:

  "JVMOptions": [
    {
      "OptionName": "pdfbox.fontcache",
      "OptionValue": "./fontcache/"
    }
  ],

seems the resolution of the path fails, probably because the current working folder is not the root of the repository expected from the cache managed of generateclasses.yaml.
A new feature shall be added to JNetReflector to resolve environment variables so it is possible to use a snippet like:

  "JVMOptions": [
    {
      "OptionName": "pdfbox.fontcache",
      "OptionValue": "$(FONTCACHE_FOLDER)"
    }
  ],