[8.15](backport #4090) Replace deprecated deployment template ID

[mergify[bot]]

This PR updates the deployment template ID used to spin up deployments in ESS for Cloud E2E tests. The deployment template ID being used has been deprecated and continuing to use it is making the Cloud E2E tests fail like so:

ec_deployment.deployment: Creating...
--
  | ╷
  | │ Error: failed creating deployment
  | │
  | │   with ec_deployment.deployment,
  | │   on main.tf line 46, in resource "ec_deployment" "deployment":
  | │   46: resource "ec_deployment" "deployment" {
  | │
  | │ api error: 10 errors occurred:
  | │   * deployments.elasticsearch_using_legacy_dt: The referenced deployment template in elasticsearch plan [gcp-io-optimized-v2] is no longer available.
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.coordinating.1] in topology element [coordinating] is no longer
  | │ available .
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.data.highio.1] in topology element [hot_content] is no longer
  | │ available .
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.data.highstorage.1] in topology element [cold] is no longer
  | │ available .
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.data.highstorage.1] in topology element [warm] is no longer
  | │ available .
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.es.datafrozen.n1.64x10x95] in topology element [frozen] is no
  | │ longer available .
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.integrationsserver.1] in topology element [<unknown>] is no
  | │ longer available .
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.kibana.1] in topology element [<unknown>] is no longer available
  | │ .
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.master.1] in topology element [master] is no longer available .
  | │   * deployments.topology_element_using_legacy_ic: The referenced instance configuration [gcp.ml.1] in topology element [ml] is no longer available .
  | │
  | │
  | ╵
  | ╷
  | │ Error: failed creating deployment

---

This is an automatic backport of pull request #4090 done by Mergify.

[ycombinator]

This PR is failing on the E2E test like so:

=== RUN   TestAgentInstallSuite
--
  | agent_install_test.go:91:
  | Error Trace:    /opt/buildkite-agent/builds/bk-agent-prod-gcp-1731506501555537000/elastic/fleet-server/testing/e2e/agent_install_test.go:140
  | /opt/buildkite-agent/builds/bk-agent-prod-gcp-1731506501555537000/elastic/fleet-server/testing/e2e/agent_install_test.go:91
  | /opt/buildkite-agent/go/pkg/mod/github.com/stretchr/testify@v1.9.0/suite/suite.go:157
  | /opt/buildkite-agent/builds/bk-agent-prod-gcp-1731506501555537000/elastic/fleet-server/testing/e2e/agent_install_test.go:58
  | Error:          Should be true
  | Test:           TestAgentInstallSuite
  | Messages:       unable to find package download
  | FAIL: TestAgentInstallSuite (11.06s)

To make this test pass, we need an 8.15.5 artifact of Elastic Agent.

[mergify[bot]]

This pull request has not been merged yet. Could you please review and merge it @ycombinator? 🙏

[ycombinator]

Closing unmerged as we no longer expect to release more 8.15.x versions from the 8.15 branch.