[improve][build] Add a default username in the image (apache#21695)

### Motivation

Add a default username in the pulsar image. When using HDFS offloader, it requires a username to transfer the file.

docker/pulsar/Dockerfile

@@ -54,6 +54,7 @@ FROM ubuntu:22.04
 ARG DEBIAN_FRONTEND=noninteractive
 ARG UBUNTU_MIRROR=http://archive.ubuntu.com/ubuntu/
 ARG UBUNTU_SECURITY_MIRROR=http://security.ubuntu.com/ubuntu/
+ARG DEFAULT_USERNAME=pulsar
 ARG JDK_MAJOR_VERSION=17
 
 # Install some utilities
@@ -106,4 +107,5 @@ RUN chmod +x /pulsar/bin/install-pulsar-client.sh
 RUN /pulsar/bin/install-pulsar-client.sh
 
 # The UID must be non-zero. Otherwise, it is arbitrary. No logic should rely on its specific value.
+RUN useradd ${DEFAULT_USERNAME} -u 10000 -g 0
 USER 10000

tests/docker-images/latest-version-image/Dockerfile

@@ -40,10 +40,6 @@ FROM apachepulsar/pulsar:latest
 # However, any processes exec'ing into the containers will run as root, by default.
 USER root
 
-# We need to define the user in order for supervisord to work correctly
-# We don't need a user defined in the public docker image, though.
-RUN adduser -u 10000 --gid 0 --disabled-login --disabled-password --gecos '' pulsar
-
 RUN rm -rf /var/lib/apt/lists/* && apt update
 
 RUN apt-get clean && apt-get update && apt-get install -y supervisor vim procps curl