fix: add user the same way as in DDEV core, fixes #22

[stasadev]

The Issue

• Fixes MacOS: Build fails with groupadd: GID '20' already exists #22

How This PR Solves The Issue

Using https://github.com/ddev/ddev/blob/4b5686665ba136867e7252cd080e9a31bc3f83d5/pkg/ddevapp/config.go#L1367-L1368 technique to fix failing build.

Manual Testing Instructions

On MacOS 15.6 + Docker Desktop:

ddev config --webserver-type=generic
ddev add-on get https://github.com/stasadev/ddev-frankenphp/tarball/refs/pull/24/head
ddev restart

$ ddev exec -s frankenphp 'whoami && id -u && id -g'
testbot
501
1000

$ ddev exec 'whoami && id -u && id -g'
testbot
501
20

Automated Testing Overview

Release/Deployment Notes

[rfay]

This seems like it should be fine. The intent is just to use the same username/uid/gid as the user on the host, but do something else if necessary.