feat: add SCL utility packages and GCC toolchain for container build

- Added `scl-utils` and `scl-utils-build` to manage software collections.
- Installed `gcc-toolset-11-toolchain` for C++ development.

Author: lkiesow

container-files/Dockerfile.el8

@@ -7,6 +7,9 @@ RUN dnf -y install https://data.lkiesow.de/opencast/maven-3.8.2-1.el8.noarch.rpm
 RUN dnf -y install \
     dnf-plugins-core \
     rpmdevtools \
+    scl-utils \
+    scl-utils-build \
+    gcc-toolset-11-toolchain \
     rpmlint \
     rpm-sign \
     createrepo \