[Fleet] Add missing package policies for managed preconfigured policies

[nchaulet]

Summary

Resolve #113921

Change the behavior of the preconfiguration service to allow to add new package policy to an already created policy.
Also I removed the deletion of the policy in case an error happen during the package policy creation as this new behavior will allow to get the package policy on the next call to setup.

How to tests

From a new kibana ES environment

start you kibana a first time with that config

xpack.fleet.packages:
  - name: apm
    version: latest
xpack.fleet.agentPolicies:
  # Cloud Agent policy
  - name: Elastic Cloud agent policy
    description: Default agent policy for agents hosted on Elastic Cloud
    is_default: false
    is_managed: true
    is_default_fleet_server: true
    namespace: default
    monitoring_enabled: []
    package_policies:
      - name: Fleet Server
        package:
          name: fleet_server
        inputs:
          - type: fleet-server
            keep_enabled: true
            vars:
              - name: host
                value: 0.0.0.0
              - name: port
                value: 8220

Than restart Kibana with that config, you should see an APM package policy in your policy

xpack.fleet.packages:
  - name: apm
    version: latest
xpack.fleet.agentPolicies:
  # Cloud Agent policy
  - name: Elastic Cloud agent policy
    description: Default agent policy for agents hosted on Elastic Cloud
    is_default: false
    is_managed: true
    is_default_fleet_server: true
    namespace: default
    monitoring_enabled: []
    package_policies:
      - name: apm-cloud-123
        package:
          name: apm
      - name: Fleet Server
        package:
          name: fleet_server
        inputs:
          - type: fleet-server
            keep_enabled: true
            vars:
              - name: host
                value: 0.0.0.0
              - name: port
                value: 8220

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[kpollich]

Tested locally and LGTM 🚀

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: bcd9488
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Metrics [docs]

✅ unchanged

History

• 💔 Build #9135 failed 7745a64
• 💚 Build #9075 succeeded 30627e9
• 💔 Build #8767 failed 859f4f6

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @nchaulet

[kibanamachine]

💚 Backport successful

Status	Branch	Result
✅	8.0

This backport PR will be merged automatically after passing CI.