fix: Revert removal of -Xms JVM option

Logstash has '-Xms1g' set inside 'config/jvm.options', so either -Xms
must be set, or -Xmx must be greater than 1g (which is too high of a
default for docker-elk).

Elastic explicitly recommends setting -Xms and -Xmx to the same value
for Elasticsearch:
  https://www.elastic.co/guide/en/elasticsearch/reference/8.2/advanced-configuration.html#set-jvm-heap-size

docker-compose.yml

@@ -36,7 +36,7 @@ services:
       - "9200:9200"
       - "9300:9300"
     environment:
-      ES_JAVA_OPTS: -Xmx512m
+      ES_JAVA_OPTS: -Xms512m -Xmx512m
       # Bootstrap password.
       # Used to initialize the keystore during the initial startup of
       # Elasticsearch. Ignored on subsequent runs.
@@ -61,7 +61,7 @@ services:
       - "5000:5000/udp"
       - "9600:9600"
     environment:
-      LS_JAVA_OPTS: -Xmx256m
+      LS_JAVA_OPTS: -Xms256m -Xmx256m
       LOGSTASH_INTERNAL_PASSWORD: ${LOGSTASH_INTERNAL_PASSWORD:-}
     networks:
       - elk