fix: set uid gid of www-data to 1000

[jokesterfr]

Questions	Answers
Description?	As suggested by the community, would be easier for Linux users to have already a 1000 www-data user, which would help while mounting local files to the docker container.
Type?	improvement
BC breaks?	no
Deprecations?	no
Fixed ticket?	Fixes #99
How to test?	docker run -it --rm --entrypoint sh prestashop/prestashop-flashlight id would give 1000.