ci: Build/sign RPMs for multiple Fedora versions

* Use `matrix` to generate pipelines for multiple Fedora versions
* Sign RPM packages using the Jenkins GPG key
* Publish RPM files to *dch* repository on *files.pyrocufflink.blue*
  instead of Gitea (the latter cannot handle multiple releases of the
  same package)

ci/prepare.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+dnf install -y \
+	--setopt install_weak_deps=0 \
+	make \
+	openssh-clients \
+	openssl-devel \
+	rpm-build \
+	rpm-sign \
+	rsync \
+    selinux-policy-devel \
+	tar \
+    xz \
+	--
+
+install -m u=rwx,go= -d "${GNUPGHOME}"
+cat > "${GNUPGHOME}"/gpg-agent.conf <<EOF
+allow-loopback-pinentry
+EOF