Add SASL/SCRAM support to the Kafka test container

[faec]

What does this PR do?

Expands the configuration of the Kafka test container so that it adds a new external port 9093 that uses SASL/SCRAM authentication.

Why is it important?

As part of making SASL/SCRAM on Kafka GA, we want to include it in the automated tests, so our Kafka test container needs to support it (and include the certificates necessary for the client to connect).

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

Create and start the container:

docker build -t kafkatest testing/environments/docker/kafka
docker run -p 127.0.0.1:9092:9092/tcp -p 127.0.0.1:9093:9093/tcp --rm --name kafkacontainer -d kafkatest

Point kafka at localhost (this is only needed to access the kafka broker from the host system, not another container, since on the Docker network the broker identifies itself by that name): edit /etc/hosts to add the line 127.0.0.1 kafka.

The server can now be accessed by beats on the host system, e.g. with this output configuration:

output.kafka:
  hosts: ["127.0.0.1:9093"]
  topic: "hello"
  protocol: "https"

  ssl.certificate_authorities: ["testing/environments/docker/kafka/certs/ca-cert"]
  sasl.mechanism: "SCRAM-SHA-512"

  username: "beats"
  password: "KafkaTest"

(the path in certificate_authorities should be modified if necessary to point at ca-cert in the test container directory).

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[mergify]

This pull request does not have a backport label. Could you fix it @faec? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2021-11-16T21:01:43.049+0000

• Duration: 101 min 5 sec

• Commit: efb736f

Test stats 🧪

Test	Results
Failed	0
Passed	54253
Skipped	5345
Total	59598

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /package : Generate the packages and run the E2E tests.

• /beats-tester : Run the installation tests with beats-tester.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[kvch]

You are a superhero! WFG.