Update docker-entrypoint.sh to latest

Summary

Open source keycloak docker images have an entrypoint script that supports the JAVA_OPTS_APPEND environment variable. This feature has been supported keycloak docker images since 12.0, but it has not been yet supported in this repository

Steps to reproduce

Run this docker image with the -e JAVA_OPTS_APPEND variable set to an option, and note that option is not recognized / appended to the /opt/jboss/keycloak/bin/standalone.conf file in the running container as is shown in https://github.com/keycloak/keycloak-containers/blob/master/server/tools/docker-entrypoint.sh#L108

What is the current bug behavior?

Options set with the JAVA_OPTS_APPEND are ignored.

What is the expected correct behavior?

The running containers should have the updated /opt/jboss/keycloak/bin/standalone.conf file, and the additional options should be seen on the running java command.

Relevant logs and/or screenshots

(Paste any relevant logs - please use code blocks (```) to format console output, logs, and code as it's very hard to read otherwise.)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem) Please port https://github.com/keycloak/keycloak-containers/blob/master/server/tools/docker-entrypoint.sh to this repository's https://repo1.dso.mil/dsop/opensource/keycloak/keycloak/-/blob/development/scripts/docker-entrypoint.sh script.

Defintion of Done

• Bug has been identified and corrected within the container

/cc @ironbank-notifications/bug