main/postmarketos-ui-phosh: add : add the scale-to-fit helper

Adds the scale-to-fit helper script from the upstream phoc project.

This allows even for apps unpatched at the source level to fit the screen of a smartphone, such as the PinePhone, increasing its utility at least while not all apps one may wish to use are patched.

Usage:

scale-to-fit <APP-ID> on // can be easily disabled with off instead

For the background rationale behind this script's inclusion, see #683 (closed)