core: rework templating

Use frep [0] which uses the Go templating capabilities.

[0]: https://github.com/subchen/frep

base/Dockerfile

@@ -4,6 +4,7 @@ ARG JITSI_RELEASE=stable
 
 ADD https://github.com/just-containers/s6-overlay/releases/download/v1.21.4.0/s6-overlay-amd64.tar.gz /tmp/s6-overlay.tar.gz
 ADD https://download.jitsi.org/jitsi-key.gpg.key /tmp/jitsi.key
+ADD https://github.com/subchen/frep/releases/download/v1.3.3/frep-1.3.3-linux-amd64 /usr/bin/frep
 
 COPY rootfs /
 
@@ -18,6 +19,7 @@ RUN \
 	apt-dpkg-wrap apt-get update && \
 	apt-dpkg-wrap apt-get dist-upgrade -y && \
 	apt-dpkg-wrap apt-get autoremove -y --purge gnupg && \
-	apt-cleanup
+	apt-cleanup && \
+	chmod +x /usr/bin/frep
 
 ENTRYPOINT [ "/init" ]

base/rootfs/usr/bin/tpl

@@ -0,0 +1,4 @@
+#!/bin/bash
+
+exec frep $1:-
+