fix: correct JVM options syntax for ELASTIC_MEMORY_SIZE

[oklien]

Description

The .env sample currently uses an uppercase G when specifying JVM heap settings via OPENSEARCH_JAVA_OPTS (for example, -Xms1G -Xmx1G).

docker/.env.sample

Line 11 in 18fdf85

ELASTIC_MEMORY_SIZE=4G

The official OpenSearch and Elasticsearch documentation consistently uses lowercase g (for example, -Xms1g -Xmx1g).

While both formats are accepted by the JVM, aligning the documentation with the examples used in OpenSearch and Elasticsearch would improve consistency and reduce confusion for users.

References:

• OpenSearch: https://docs.opensearch.org/latest/install-and-configure/install-opensearch/index/
• Elasticsearch JVM settings: https://www.elastic.co/docs/reference/elasticsearch/jvm-settings