Make nomulus work locally (#2349)

Chose the default transaction manager based on RegistryEnvironment. This
makes it possible to run nomulus on Jetty locally. Tested with the
following:

```bash
./gradle :jetty:run -Penvironment=alpha
curl http://localhost:8080/beta.app
```

The docker image is also updated to take an argument that specifies the
environment. It runs locally as well but the container doesn't get
access to locally stored credentials, so it fails to initialize the
transaction manager.

jetty/Dockerfile

@@ -1,7 +1,5 @@
 FROM jetty:12-jdk21
 ADD --chown=jetty:jetty build/jetty-base /jetty-base
-ENV JETTY_BASE=/jetty-base
-WORKDIR "$JETTY_BASE"
+ADD --chown=jetty:jetty start.sh /
 EXPOSE 8080
-ENTRYPOINT ["java", "-jar", "/usr/local/jetty/start.jar"]
-
+ENTRYPOINT ["/bin/sh", "/start.sh"]