AE-1820: Enable Shared Strings Table on .xlsx inventory writer to save memory

[YanWittmann]

This PR saves memory when writing .xlsx inventory files by enabling the Shared String Table feature on the apache POI worksheet that is being written.

// before
final SXSSFWorkbook workbook = new SXSSFWorkbook();
// last parameter is useSharedStringsTable
final SXSSFWorkbook workbook = new SXSSFWorkbook(null, 100, true, true);

As the string table only supports XSSFRichTextString, I had to switch to that one (does not support the currently used HSSFRichTextString).

After vs. Before:

[YanWittmann]

This change will only impact the XLSX format, not XLS, as the table is not available for XLS.