Add new subcommand to help using stacks not managed by elastic-package

[jsoriano]

Problem statement

There are some use cases that require customizations of the elastic stack that elastic-package doesn't support. A relatively common use case is when developing features in Elasticsearch, Kibana or other internal components. Wwe could add more providers to elastic-package stack up, but this can be quite difficult to maintain, as each developer environment can have very different dependencies, and backwards compatibility may not be granted.

At the moment a common workaround for that is to set the related ELASTIC_PACKAGE_ environment variables. But this is not very obvious and doesn't have such a good integration with other elastic-package subcommands.

Proposed solution

Add a new command that helps with the configuration of a profile to reuse an stack not managed by elastic-package.

It could be something like the following:

elastic-package stack import --elasticsearch-host http://localhost:9201 --kibana-host http://localhost:5601/xyz

This command would configure the profile so the stack/config.json file contains something like the following:

{
  "provider": "import",
  "elasticsearch_host": "https://127.0.0.1:9201",
  "elasticsearch_username": "elastic",
  "elasticsearch_password": "changeme",
  "kibana_host": "http://127.0.0.1:5601/xyz",
  "ca_cert_file": ""
}

A flag would exist for each of these variables with the usual defaults:

• --elasticsearch-host: http://localhost:9200
• --elasticsearch-username: elastic
• --elasticsearch-password: changeme
• --kibana-host: http://localhost:5601
• --ca-cert-file: `` (not set)

Ideally we should support other authentication methods like API keys, but lets leave this as a separate issue by now (see #1633).

We should check that elastic-package commands are able to work with this stack configuration:

• elastic-package shellinit should print the configured values.
• elastic-package status could check if services are reachable.
• elastic-package test should work.