Refactor Dockerfile to reduce the amount of layers

[AchimGrolimund]

PR Description

Reduce the layers in the Docker image by 8 Layers. This also reduces the size of the Docker image

Which issue(s) this PR fixes

Notes to the Reviewer

PR Checklist

• CHANGELOG.md updated
• Documentation added
• Tests updated
• Config converters updated

[henworth]

Hopeful this change can get looked at, just started testing migrating my agents to alloy and CI flagged the amount of wasted space in the image build.

[henworth]

I'd remove the line break and indent 2 more spaces, looks a bit cleaner IMO.

Suggested change

	RUN groupadd --gid $UID $USERNAME
	RUN useradd -m -u $UID -g $UID $USERNAME
	RUN chown -R $USERNAME:$USERNAME /etc/alloy
	RUN chown -R $USERNAME:$USERNAME /bin/alloy
	RUN groupadd --gid $UID $USERNAME \
	&& useradd -m -u $UID -g $UID $USERNAME \
	&& chown -R $USERNAME:$USERNAME /etc/alloy \
	&& chown -R $USERNAME:$USERNAME /bin/alloy \
	&& mkdir -p /var/lib/alloy/data \
	&& chown -R $USERNAME:$USERNAME /var/lib/alloy \
	&& chmod -R 770 /var/lib/alloy
	RUN mkdir -p /var/lib/alloy/data
	RUN chown -R $USERNAME:$USERNAME /var/lib/alloy
	RUN chmod -R 770 /var/lib/alloy
	RUN groupadd --gid $UID $USERNAME \
	&& useradd -m -u $UID -g $UID $USERNAME \
	&& chown -R $USERNAME:$USERNAME /etc/alloy \
	&& chown -R $USERNAME:$USERNAME /bin/alloy \
	&& mkdir -p /var/lib/alloy/data \
	&& chown -R $USERNAME:$USERNAME /var/lib/alloy \
	&& chmod -R 770 /var/lib/alloy