Fix TestLogIngestionFleetManaged, TestDebLogIngestFleetManaged

[belimawr]

[Integration Tests] Generate namespace based on UUIDv4

What does this PR do?

TestLogIngestionFleetManaged was failing because the namespace generated by the integration tests framework was not unique among different tests and test runs, so sometimes collisions would occurs causing some tests to be flaky.

TestDebLogIngestFleetManaged was failing because it also has got Beats logging connection errors before receiving the configuration from Elastic-Agent, now this message is also in the allow list.

When testing .deb the AGENT_KEEP_INSTALLED environment variable is respected.

When an integration test fails, the work directory created by the framework is now kept and its path is printed.

Why is it important?

It fixes flakiness in our tests

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

## Disruptive User Impact

How to test this PR locally

Run an integration test: mage -v integration:single TestLogIngestionFleetManaged

Related issues

• Closes [Flaky Test]: TestLogIngestionFleetManaged, TestDebLogIngestFleetManaged – list of error messages is expected to be empty #5372

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?
• ...

[elasticmachine]

Pinging @elastic/elastic-agent (Team:Elastic-Agent)

[mergify]

This pull request does not have a backport label. Could you fix it @belimawr? 🙏
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 8./d branch. /d is the digit

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

[belimawr]

/test

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[jlind23]

Force merging this PR to get main back to an healthy state.

Here the TestEvenLogFile failed on windows with this error which is unrelated to those change :

{"Time":"2024-09-02T14:24:00.640065Z","Action":"output","Package":"github.com/elastic/elastic-agent/testing/integration(windows-amd64-2022-default)","Test":"TestEventLogFile","Output":"    fixture.go:1213: could not remove temp dir 'C:\\Users\\windows\\AppData\\Local\\Temp\\TestEventLogFile1663512932': remove C:\\Users\\windows\\AppData\\Local\\Temp\\TestEventLogFile1663512932\\elastic-agent-8.16.0-SNAPSHOT-windows-x86_64\\data\\elastic-agent-dd44f5\\components\\agentbeat.exe: Access is denied.\n"}