fix: agent directories must belong to root

[mdelapenya]

• chore: store agent pat into the metadata struct of the agent package
• chore: create agent directories for UNIX-based agent installers

What does this PR do?

It adds a new field in the struct representing the agent metadata to store the base path where the agent will be installed under Linux/Darwin systems.

This path will be created in the target system at the PreInstall phase, so that it has the right permissions beforehand.

Why is it important?

This agent path, according to elastic/elastic-agent#398, must belong to root. And this applies only to 8.3 and main.

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 run the Unit tests (make unit-test), and they are passing locally
• I have run the End-2-End tests for the suite I'm working on, and they are passing locally
• I have noticed new Go dependencies (run make notice in the proper directory)

Related issues

• Consequence of Agent configuration encryption elastic-agent#398
• Discovered while testing [automation] update elastic stack version for testing 8.4.0-481759a3 #2585 and [automation] update elastic stack version for testing 8.3.0-4644f7c7 #2586

[elasticmachine]

💔 Tests Failed

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Build stats

• Start Time: 2022-06-01T14:50:24.112+0000

• Duration: 92 min 9 sec

Test stats 🧪

Test	Results
Failed	1
Passed	308
Skipped	0
Total	309

Test errors

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Initializing / End-To-End Tests / kubernetes-autodiscover_debian_amd64_elastic-agent / [empty] – TEST-kubernetes-autodiscover_debian_amd64_elastic-agent-3726dfb8-2022-06-01-15:44:13.xml

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 Test report file /var/lib/jenkins/workspace/PR-2590-2-338bd586-9160-416b-872a-f61b458cc51e/outputs/3.16.159.150/TEST-kubernetes-autodiscover_debian_amd64_elastic-agent-3726dfb8-2022-06-01-15:44:13.xml was length 0 

Steps errors

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Executing ansible-playbook

• Took 22 min 21 sec . View more details here
• Description: /var/lib/jenkins/workspace/2e-tests_e2e-testing-mbp_PR-2590/.venv/bin/ansible-playbook --private-key="/var/lib/jenkins/workspace/2e-tests_e2e-testing-mbp_PR-2590/src/github.com/elastic/e2e-testing/e2essh" --extra-vars="workspace=/var/lib/jenkins/workspace/2e-tests_e2e-testing-mbp_PR-2590/src/github.com/elastic/e2e-testing/ runId=a1577a69 sshPublicKey=/var/lib/jenkins/workspace/2e-tests_e2e-testing-mbp_PR-2590/src/github.com/elastic/e2e-testing/e2essh.pub" --ssh-common-args='-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null' /var/lib/jenkins/workspace/2e-tests_e2e-testing-mbp_PR-2590/src/github.com/elastic/e2e-testing/.ci/ansible/playbook.yml -i "3.20.238.84," -t setup-stack --extra-vars="buildURL=https://beats-ci.elastic.co/job/e2e-tests/job/e2e-testing-mbp/job/PR-2590/2/ gitSha=3bd7516c7716291d4e014a8cda7b2e3ead4e56b9 build=2 repo=e2e-testing branch=pr-2590 type=ci stackRunner=3.20.238.84 nodeLabel=stack nodeUser=admin nodeImage=ami-0d90bed76900e679a nodeInstanceType=t3.xlarge"

Sleep

• Took 0 min 5 sec . View more details here
• Description: 5

🐛 Flaky test report

❕ There are test failures but not known flaky tests.

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Genuine test errors

💔 There are test failures but not known flaky tests, most likely a genuine test failure.

• Name: Initializing / End-To-End Tests / kubernetes-autodiscover_debian_amd64_elastic-agent / [empty] – TEST-kubernetes-autodiscover_debian_amd64_elastic-agent-3726dfb8-2022-06-01-15:44:13.xml

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