MAGECLOUD-4164 [Spike] Investigate issue with elasticsearch image on AWS

[arhiopterecs]

Description

Added option --es-env-var for docker-compose.yml file generator. Using this option, you can specify the environment variables that will be applied when starting the Elasticsearch container.
This will allow you to change service settings, such as heap size for JVM or Elasticsearch options.
Parameter changes for JVM are available from image version 1.7
Changing Elasticsearch parameters using environment variables is available starting from version 5.2

Fixed Issues (if relevant)

1. https://magento2.atlassian.net/browse/MAGECLOUD-4164

Manual testing scenarios

1. Clone [magento-cloud template](https://github.com/magento/magento-cloud).
2. Run: $ composer update in the magento-cloud template directory:
3. Generate the docker-compose.yml file with env variables for elasticsearch service:

$ php vendor/bin/ece-docker build:compose --es-env-var=ES_JAVA_OPTS="-Xms512m -Xmx512m" --es-env-var=node.store.allow_mmapfs=false
Configuration was built.

NOTE: By default, an image with Elasticsearch version 6.5 is used. For this version of Elasticsearch, the option node.store.allow_mmapfs exists.
For image varsions 5.2, 2.4, 1.7 ,this option does not exist
Forimage varsions 7.5, this parameter was renamed to node.store.allow_mmap
4. Check the file docker-compose.yml, the following settings must exist:

... 
elasticsearch:
    hostname: elasticsearch.magento2.docker
    image: 'magento/magento-cloud-docker-elasticsearch:6.5-1.1'
    environment:
      - 'ES_JAVA_OPTS=-Xms512m -Xmx512m'
      - node.store.allow_mmapfs=false
    networks:
      magento:
        aliases:
          - elasticsearch.magento2.docker           
....  

5. Run: $ docker-compose up -d. Containers started successfully
6. Login in elasticsearch container:

$ docker-compose exec elasticsearch bash

7. Run the command in the container: $ ps aux | grep -E "(Xms|Xmx)"
   Expected: The last values ​​of the -Xms and -Xmx parameters are 512m

8. Run the command in the container: $ curl http://localhost:9200/_nodes 2>&1 | grep 'mmapfs'.
   Expected:"allow_mmapfs":"false" should be present

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages

[NadiyaS]

 It would be good to add example for this option.

[shiftedreality]

Please use single quotes

[shiftedreality]

I believe it's also optional by default

[arhiopterecs]

Done

[shiftedreality]

EVN => ENV

[shiftedreality]

Please use full name, OPTION_ES_ENVIRONMENT_VARIABLE

[arhiopterecs]

Done

[shiftedreality]

I would also suggest dropping env part, variables are already self-explaining

[arhiopterecs]

Done

[arhiopterecs]

PR was recreated #174