Add ability to enroll with defined ID and replace_token

[blakerouse]

What does this PR do?

Adds new --id (ELASTIC_AGENT_ID env for container) and --replace-token (FLEET_REPLACE_TOKEN env for container) to enrollment.

Why is it important?

Allows an Elastic Agent to enroll with a defined ID and replacement token to allow it to replace an existing Elastic Agent. The original Elastic Agent must have also been enrolled with the same --replace-token or it will not be allow to enroll if the --id collides with an existing Elastic Agent.

Checklist

• I have read and understood the pull request guidelines of this project.
• 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 (no config changes)
• [ ] I have added tests that prove my fix is effective or that my feature works (cannot unit test)
• 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

You need this PR (elastic/fleet-server#4290) from Fleet Server and have that Fleet Server running to enroll. Then you can build this PR and run enroll with --id and --replace-token.

Related issues

• Closes Add ability to define the specific agent-id during enroll #6361

[mergify]

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

• backport-./d./d is the label to automatically backport to the 8./d branch. /d is the digit

[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.

[elasticmachine]

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

[elastic-sonarqube]

Quality Gate passed

Issues
4 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
66.1% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube

[jlind23]

@theletterf @nimarezainia do we have any follow up actions here in order to document this for Kubernetes use case at least?
cc @ebeahan

[nimarezainia]

@theletterf @nimarezainia do we have any follow up actions here in order to document this for Kubernetes use case at least? cc @ebeahan

@jlind23 I don't see an issue if we wanted to document this option for users who want to reuse the agent.id - but we haven't documented this yet as far as I know.

[theletterf]

I take this is for Elastic Agent docs, not EDOT docs, right? I'd be happy to review a docs PR on this.

[nimarezainia]

yes at the moment only applies to elastic agent docs.

[jlind23]

@nimarezainia are you taking this one or shall I kindly ask @ebeahan to find someone?

[nimarezainia]

@jlind23 maybe I'm confused. This ask is for just documentation of the install flag --replace-token and the description above by Blake is explaining it well.

[theletterf]

I guess Julien was hinting precisely at who would open the documentation PR. :)

I'll check with the team and see to it.

[vishaangelova]

I’ve created a docs issue to document this, so it’s on our radar.