Add Ubuntu Hirsute

hirsute/x86_64/Dockerfile

@@ -2,15 +2,19 @@ FROM ubuntu:hirsute
 
 ENV DEBIAN_FRONTEND=noninteractive
 
+# absolute apt-get path because: eatmydata: unable to find 'apt-get' in PATH
 RUN apt-get update \
  && apt-get install -y eatmydata \
- && eatmydata /usr/bin/apt-get upgrade -y # eatmydata: unable to find 'apt-get' in PATH
+ && eatmydata /usr/bin/apt-get upgrade -y
 
 RUN eatmydata /usr/bin/apt-get install -y \
   sudo wget curl tar expect git \
   devscripts build-essential lintian ccache pbuilder aptitude apt-utils
 
-RUN curl https://packages.icinga.com/icinga.key | apt-key add - \
+# not apt-key add because:
+# E: gnupg, gnupg2 and gnupg1 do not seem to be installed, but one of them is required for this operation
+RUN eatmydata /usr/bin/apt-get install -y gnupg2 \
+ && curl https://packages.icinga.com/icinga.key | gpg --dearmor -o /usr/share/keyrings/icinga-archive-keyring.gpg \
  && DIST="$(lsb_release -sc)" \
  && echo "deb http://packages.icinga.com/ubuntu icinga-${DIST} main" > /etc/apt/sources.list.d/${DIST}-icinga.list