Allow "Enable CORS" within GeoServer container through env

[afabiani]

I would like to be able to enable CORS on GeoServer by using the .env or the Docker ARGs like:

CORS_ENABLED=true
CORS_ALLOWED_ORIGINS=*
CORS_ALLOWED_METHODS=GET,POST,PUT,DELETE,HEAD,OPTIONS
CORS_ALLOWED_HEADERS=*

If enabled the entrypoint.sh should be able to automatically patch the WEB-INF/web.xml file as follows:

if [ "${CORS_ENABLED}" = "true" ]; then
  if ! grep -q DockerGeoServerCorsFilter "$CATALINA_HOME/webapps/geoserver/WEB-INF/web.xml"; then
    echo "Enable CORS for $CATALINA_HOME/webapps/geoserver/WEB-INF/web.xml"
    sed -i "\:</web-app>:i\\
    <filter>\n\
      <filter-name>DockerGeoServerCorsFilter</filter-name>\n\
      <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>\n\
      <init-param>\n\
          <param-name>cors.allowed.origins</param-name>\n\
          <param-value>${CORS_ALLOWED_ORIGINS}</param-value>\n\
      </init-param>\n\
      <init-param>\n\
          <param-name>cors.allowed.methods</param-name>\n\
          <param-value>${CORS_ALLOWED_METHODS}</param-value>\n\
      </init-param>\n\
      <init-param>\n\
        <param-name>cors.allowed.headers</param-name>\n\
        <param-value>${CORS_ALLOWED_HEADERS}</param-value>\n\
      </init-param>\n\
    </filter>\n\
    <filter-mapping>\n\
      <filter-name>DockerGeoServerCorsFilter</filter-name>\n\
      <url-pattern>/*</url-pattern>\n\
    </filter-mapping>" "$CATALINA_HOME/webapps/geoserver/WEB-INF/web.xml";
  fi
fi