[Etherpad] Automatic PG database creation and healthcheck in entrypoint

pica-etherpad/Dockerfile

@@ -60,7 +60,7 @@ RUN useradd --uid ${UID} --create-home etherpad
 COPY --from=downloader --chown=etherpad /opt/etherpad-lite /opt/etherpad-lite/
 
 RUN apt-get update && \
-    apt-get install -y curl default-mysql-client && \
+    apt-get install -y curl default-mysql-client postgresql-client && \
     chmod +x /opt/etherpad-lite/entrypoint.sh && \
     usermod -d /opt/etherpad-lite etherpad && \
     chown -R etherpad /opt/etherpad-lite && \

pica-etherpad/entrypoint.sh

@@ -22,7 +22,7 @@ if [ -z "${DB_HOST}" ]; then
 	exit 1
 fi
 
-while ! mysqladmin ping -u${DB_USER} -p${DB_PASSWORD} -h"${DB_HOST}" &>/dev/null; do
+while ! { mysqladmin ping -u${DB_USER} -p${DB_PASSWORD} -h"${DB_HOST}" &>/dev/null || PGPASSWORD=${DB_PASSWORD} psql -h${DB_HOST} -U${DB_USER} -c "SELECT 1" }; do
 		echo "Database server not ready yet, re-trying in 5 seconds..."
     sleep 5
 done

pica-etherpad/secrets/etherpad-week-db.secrets.example

 POSTGRES_PASSWORD=password
+POSTGRES_USER=etherpad
+POSTGRES_DB=etherpad-lite