smoke: Fix smoke test Terraform issue

[ericywl]

Motivation/summary

Fix smoke test issue:

-> Adding tfvar integrations_server="false"
-> Applying terraform configuration...

Error: Invalid index

  on ../../infra/terraform/modules/ec_deployment/outputs.tf line 53, in output "apm_component_id":
  53:   value       = ec_deployment.deployment.integrations_server[0].resource_id
    ├────────────────
    │ ec_deployment.deployment.integrations_server is empty list of object

The given key does not identify an element in this collection value: the
collection has no elements.

Error: Invalid index

  on ../../infra/terraform/modules/ec_deployment/outputs.tf line 58, in output "fleet_component_id":
  58:   value       = ec_deployment.deployment.integrations_server[0].resource_id
    ├────────────────
    │ ec_deployment.deployment.integrations_server is empty list of object

The given key does not identify an element in this collection value: the
collection has no elements.

How to test these changes

Run smoke test again.

Test run: https://github.com/elastic/apm-server/actions/runs/13560141549, it seems the usual ones are passing again.

[ericywl]

[For reviewers] Not sure what this should fallback to

[ericywl]

@endorama Do you have any idea?

[simitt]

Why is the distinction between integrations_server and apm resource even bleeding into our code? Having one variable defined in terraform that abstracts this sound the right path forward. @ericywl you are on a good path here already, adding the fallback for apm resource. @endorama is there any reason why apm_component_id and fleet_component_id would be needed? (Given that they currently point to the same resource I would not think so).

Quick recap: in cloud the old resource was apm, and the newer one (introduced in 8.0) is integrations_server. Currently both can exist, for deployments created in 7.x the resource will be apm, for newer deployments resource will be integrations_server (if not explicitly migrated, which we don't do here).

[mergify]

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

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-9./d is the label to automatically backport to the 9./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[ericywl]

Seems like there is still this issue (which is from before?):

Error: failed tracking create progress: 2 errors occurred:
	* found deployment plan errors: deployment [2ae8abcda33623d520648761a5f7b15a] - [apm][15bf782c863f4d8886efe95cc106e386]: caught error: "Plan change failed: Some instances were not running"
	* set "request_id" to "h8e5sbnwngz1qquqj7wm0a8emq4pqj9n4sgcwryug2ga41ljtkobsc49l4d7ruuy" to recreate the deployment resources

  with module.ec_deployment.ec_deployment.deployment,
  on ../../infra/terraform/modules/ec_deployment/deployment.tf line 17, in resource "ec_deployment" "deployment":
  17: resource "ec_deployment" "deployment" {