Fix debian packaging for upgrades

[blakerouse]

What does this PR do?

Fixes the debian packaging to properly copy the state.enc and state.yml files to the new version of the Elastic Agent.

Why is it important?

Without this upgrading to a new version of the Elastic Agent losses the state.enc and/or state.yml file.

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 (cannot add unit tests for packaging)
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

None

How to test this PR locally

Build the debian package:

$ PLATFORMS="linux/amd64" PACKAGES="deb" SNAPSHOT="true" EXTERNAL="true" mage package

Install older version of Elastic Agent

sudo dpkg -D2 -i elastic-agent-8.14.3-amd64.deb

Enroll into Fleet

sudo elastic-agent enroll --url={url} --enrollment-token={token}

Upgrade to built version

sudo dpkg -D2 -i build/distributions/elastic-agent-8.16.0-SNAPSHOT-amd64.deb

Related issues

• Closes Agent .deb install: state.enc not copied during Elastic Agent upgrade from 8.13 and above #5101

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[pierrehilbert]

That was fast haha

[blakerouse]

@pierrehilbert I said I had it ready, I just need to add an integration test. I also want to test this change with RPM's as well.

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarQube

[blakerouse]

I am getting failures from flaky tests, no failures from DEB/RPM tests or the new upgrade tests. This is ready to be merged, but will need a force merge as the flaky tests have seem to become very consistent now.

[ycombinator]

I am getting failures from flaky tests, no failures from DEB/RPM tests or the new upgrade tests. This is ready to be merged, but will need a force merge as the flaky tests have seem to become very consistent now.

The failing test is the same K8s test that has been failing for a while now: #5275. As such, I'm OK to force merge this PR here.