ioc: add stage without IOC building.

This allows us to run an IOC which was built along with its support
module. This pattern is used for some community modules, including
motor's and areaDetector's ones.

A new (empty) stage has been created only to specify the base image in
the COPY command, since `--from` argument does not support variable
expansion [1].

`build-stage` has been moved below `no-build` stage, so bad multi-stage
resolvers won't fail for the new stage.

[1]: https://forums.docker.com/t/how-can-i-expand-a-variable-within-a-copy-command-in-the-dockerfile/113538/2

Dockerfile

@@ -1,21 +1,8 @@
 ARG DEBIAN_VERSION=11.7
 
-FROM ghcr.io/cnpem/lnls-debian-11-epics-7:v0.3.0 AS build-stage
+FROM ghcr.io/cnpem/lnls-debian-11-epics-7:v0.3.0 AS build-image
 
-ARG REPONAME
-ARG BUILD_PACKAGES
-
-RUN if [ -n "$BUILD_PACKAGES" ]; then apt update && apt install $BUILD_PACKAGES; fi
-
-WORKDIR /opt/${REPONAME}
-
-COPY . .
-
-RUN cp /opt/epics/RELEASE configure/RELEASE
-RUN rm -rf .git/
-
-
-FROM debian:${DEBIAN_VERSION}-slim as base
+FROM debian:${DEBIAN_VERSION}-slim AS base
 
 ARG RUNDIR
 ARG ENTRYPOINT=/bin/bash
@@ -38,6 +25,26 @@ RUN ln -s ${ENTRYPOINT} ./entrypoint
 ENTRYPOINT ["./entrypoint"]
 
 
+FROM base AS no-build
+
+COPY --from=build-image /opt /opt
+
+
+FROM build-image AS build-stage
+
+ARG REPONAME
+ARG BUILD_PACKAGES
+
+RUN if [ -n "$BUILD_PACKAGES" ]; then apt update && apt install $BUILD_PACKAGES; fi
+
+WORKDIR /opt/${REPONAME}
+
+COPY . .
+
+RUN cp /opt/epics/RELEASE configure/RELEASE
+RUN rm -rf .git/
+
+
 FROM build-stage AS dynamic-build
 
 ARG JOBS=1