Support API Key as environment variable

[ruflin]

Currently if connecting elastic-package to a remote Elastic Stack, only username / password as environment variable are supported. As we are moving more and more to API Keys, also an API key should be supported. See #1627 for more discussions.

Stretch goal: Ideally we would have an easy way to create an API Key either through and API call or in the UI in Kibana with the right permissions ...

[jsoriano]

There are currently issues installing packages with API keys elastic/kibana#166473

[bhapas]

@jsoriano Is this unblocked when elastic/kibana#178120 is merged?

[jsoriano]

@jsoriano Is this unblocked when elastic/kibana#178120 is merged?

Looks like that, yes.

[andrewkroh]

We need API key support for interacting with Serverless projects. Unless you create the project through the API you won't have an admin user/pass and you cannot create local users. So API key is the only option.

I hacked on this for a few minutes at andrewkroh@6e7f9c2 and was able to do some operations like install packages on serverless, but hit other issues for system tests.