Split packaging into separate steps

[oakrizan]

What does this PR do?

Splitting centralized packaging step into separate steps to speed up builds

Buildkite builds: https://buildkite.com/elastic/elastic-agent-extended-testing/builds?branch=split-packaging

Why is it important?

Since the integration test steps are divided by platforms, we can divide packaging into the corresponding steps and run integration tests for the platform as soon as the required artifacts are built without waiting for the rest.

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/fragments using the changelog tool
• I have added an integration test or an E2E test

Related issues

• Relates: https://github.com/elastic/ingest-dev/issues/4712

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[mergify]

backport-v8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarQube

[pazone]

NIT: Can we use the group key instead of mentioning all the steps?

[pazone]

I'd recommend returning those variables to the packaging script to reduce the scope