Predefining file names of PDF reports

[aronmolnar]

When PDF report is generated, we currently pre-fill the report filename in the text box and use the project title and append _report.pdf.

Companies might want to customise that filename structure to consolidate filenames across reports.
We could implement this using a Django Template syntax, as we already implemented for the project numbers plugin.

One drawback with this approach would be, however, the syntax which is different from the report designs (Django Template language vs HTML/VueJS).