Dockerfiles: update default user context

[nicoprow]

Match default user context with the default security context of the BPDM Pool and Gate Helm Charts.

Relevant Issue: #110

[FaGru3n]

LGTM

[FaGru3n]

Hi @nicoprow found out that it failed to build the docker file and i would suggest its depening on creating an system user (-S $USERNAME )with id over 100

ERROR: failed to solve: executor failed running [/bin/sh -c addgroup --gid $GID -S $USERNAME && adduser --uid $USERID --gid $GID -m $USERNAME]: exit code: 1
Error: buildx failed with: ERROR: failed to solve: executor failed running [/bin/sh -c addgroup --gid $GID -S $USERNAME && adduser --uid $USERID --gid $GID -m $USERNAME]: exit code: 1

Maybe you can adapt the example from auto-setup;
https://github.com/eclipse-tractusx/autosetup-backend/blob/4ca133ec4f3aa8df850ef7afdf3827b4f1550cd3/Dockerfile#LL39C1-L47C15

ARG USERNAME=bpdm
ARG USER_UID=100
ARG USER_GID=3000

# Create the user
RUN groupadd --gid $USER_GID $USERNAME \
    && useradd --uid $USER_UID --gid $USER_GID -m $USERNAME 

USER $USERNAME

or just removing the -Sto prevent also changing the security context in your 'deploment.yaml'

[nicoprow]

Updated the groupadd and useradd commands to work with alpine distribution