fix: enable gracefully stopping Docker container (#554)

The pre-built Docker image had two minor problems:
1. It could not be built on M1 Macs, because the internal build container used an '-alpine'
   image, which do not support the M1 architecture.
2. Docker containers based on this image could not be gracefully stopped because these used
   `eval` instead of `exec`. This again means that PGAdapter itself was started as a subprocess
   in the container, and the sigterm signal is not propagated to any subprocess inside the
   container.

Fixes #552 and #553

build/Dockerfile

@@ -2,7 +2,7 @@
 #                                     BUILD                                    #
 ################################################################################
 
-FROM maven:3.8.4-eclipse-temurin-17-alpine AS build
+FROM maven:3.8.6-eclipse-temurin-17 AS build
 
 # Copy over build files to docker image.
 COPY LICENSE ./

build/startup.sh

@@ -15,4 +15,4 @@ done
 cd /home/pgadapter
 COMMAND="java ${JAVA_ARGUMENTS} -jar pgadapter.jar ${ARGUMENTS}"
 echo $COMMAND
-eval " $COMMAND"
+exec $COMMAND