[Feature] Make "About FreshRSS" customizable

Please consider making the "About FreshRSS" page and link customizable.

Since I am using FreshRSS as a public RSS aggregator, it would be great to be able to make use of the about page for explaining what the site is for, insert an imprint and also the privacy policy. The text that is already in there could be mandatory and appended to the end. Please also consider to make the link text also customizable, e.g. "About / Privacy".

A solution could be a user editable Markdown file with a directive that sets the link text.

This could also be a solution for https://github.com/FreshRSS/FreshRSS/issues/5189

Thanks!