Add a mechanism to define content of portfolio in data file or similar

[suchja]

Currently all content of the portfolio section is defined in plain HTML in the _index-portfolio.cshtml file. To provide a better experience of this theme for "non-developers", it would be great to define the different portfolio "cards" in a separate data file or something like this. So the user would only need to add their content there and it is automatically added to the portfolio section.

Based on Statiq's Data File capabilities this is probably not really difficult.