replace dumb-init with tini for consistency among personal projects

https://github.com/fphammerle/docker-borgbackup-sshd/blob/63445c524ad9471e1208666fb041c5d0623406db/Dockerfile

Dockerfile

@@ -1,18 +1,18 @@
 FROM alpine:3.13.4
 
-ARG DUMB_INIT_PACKAGE_VERSION=1.2.5-r0
 ARG MARIADB_CLIENT_PACKAGE_VERSION=10.5.8-r0
 ARG OPENSSH_PACKAGE_VERSION=8.4_p1-r3
+ARG TINI_PACKAGE_VERSION=0.19.0-r0
 RUN apk add --no-cache \
-        dumb-init=$DUMB_INIT_PACKAGE_VERSION \
         mariadb-client=$MARIADB_CLIENT_PACKAGE_VERSION \
         openssh-server=$OPENSSH_PACKAGE_VERSION \
+        tini=$TINI_PACKAGE_VERSION \
     && adduser -S dump
 
 # RUN apk add --no-cache man openssh-doc=$OPENSSH_PACKAGE_VERSION
 
 COPY entrypoint.sh /
-ENTRYPOINT ["dumb-init", "--", "/entrypoint.sh"]
+ENTRYPOINT ["/sbin/tini", "--", "/entrypoint.sh"]
 COPY sshd_config /etc/ssh/sshd_config
 ENV SSHD_HOST_KEYS_DIR /etc/ssh/host_keys
 ENV MYSQLDUMP_ARGS --help