fix(docker): set WORKDIR to root in loki Dockerfiles

The distroless static image has workdir set to /home/nonroot, owned by the user
nonroot with uid of 65532 and permission of 700. Since the user is changed to
loki with uid 1001, this can cause the startup of container to fail, as there is
no permission to enter the workdir.

Author: umglurf

cmd/loki/Dockerfile

@@ -26,6 +26,7 @@ COPY --from=filesystem /etc/passwd /etc/passwd
 COPY --from=filesystem /etc/group /etc/group
 
 USER 10001
+WORKDIR /
 EXPOSE 3100
 ENTRYPOINT [ "/usr/bin/loki" ]
 CMD ["-config.file=/etc/loki/local-config.yaml"]

cmd/loki/Dockerfile.cross

@@ -28,6 +28,7 @@ COPY --from=filesystem /etc/passwd /etc/passwd
 COPY --from=filesystem /etc/group /etc/group
 
 USER 10001
+WORKDIR /
 EXPOSE 3100
 ENTRYPOINT [ "/usr/bin/loki" ]
 CMD ["-config.file=/etc/loki/local-config.yaml"]