[8.x](backport #2493) [Cloud Security] [Agentless] Add the creation of an agentless agent via Agentless API in the GHA Create Environment (new)

[mergify]

Summary of your changes

This change refactors the CreateEnvironment workflow to create an agentless-agent using the Agentless-API.

This should only be merged when production Serverless projects in the test region have the Agentless-API configuration in Kibana.

We enable this for ESS by simply setting the TEST_AGENTLESS to true.

Testing

To test this run the CreateEnvironment workflow with the following parameters

• Workflow branch: 10463-create-agentless-agent
• Stack version: 8.16.0-SNAPSHOT
• Select Run UI sanity tests after provision checkbox
• Kibana UI test branch: 10269-gha-sanity-tests-for-agentless-ess-deployments

(First time doing Python, be gentle 😄 )

Related Issues

• https://github.com/elastic/security-team/issues/10269
• closes https://github.com/elastic/security-team/issues/10463

Checklist

• I have added tests that prove my fix is effective or that my feature works
  • not sure if this is needed for workflow changes

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This is an automatic backport of pull request #2493 done by [Mergify](https://mergify.com).