[Fleet] Changes to bulk upgrade api for allowing rolling upgrades

[criamico]

Summary

Part of #130259

Change restrictions in the bulk upgrade API:

• Allow to upgrade to a version <= Kibana version (it was only to the exact same version before)
• Add a check related to the max fleet server version installed:
  • When no fleet server agents are being upgraded, verify that target version > maximum installed Fleet server version
  • When some fleet server agents are among the agents being upgraded, skip the fleet server version check

I'm having some trouble with the integration tests, however I put the PR up for review since the code is completed.

Testing

Test 1

• Try to update some installed agents to a version <= Kibana Version. Make sure that the fleet server agents have the same version as Kibana. From dev tools:

  POST kbn:/api/fleet/agents/bulk_upgrade
  {
    "agents": ["agent-id-1"],
    "version": "8.3.0"
  }
  

The endpoint should return 200.

• If you try with a version > Kibana it should return 400 instead.

Test 2

• Install a fleet server agent with an older version than Kibana (for example 8.1.0)
• Try to update to an higher version:

POST kbn:/api/fleet/agents/bulk_upgrade
{
  "agents": ["agent-id-1"],
  "version": "8.3.0"
}

The endpoint should return 400

Test 3

• Keeping the fleet server agent on an older version than Kibana (for example 8.1.0)
• Try to update some agents and the fleet server agent itself to an higher version:

POST kbn:/api/fleet/agents/bulk_upgrade
{
  "agents": ["agent-id-1", "fleet-server-agent-id"],
  "version": "8.3.0"
}

The endpoint should return 200

[criamico]

@elasticmachine merge upstream

[criamico]

@elasticmachine merge upstream

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[nchaulet]

I am wondering if we should move this check inside the upgrade service in the isUpgradable function

[nchaulet]

@elasticmachine merge upstream

[kibana-ci]

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Metrics [docs]

✅ unchanged

History

• 💚 Build #44752 succeeded 555a1df
• 💔 Build #44527 failed e146bec
• 💔 Build #44500 failed 743a4bf
• 💔 Build #44456 failed 3f59d67
• 💔 Build #44366 failed aca1c0b
• 💔 Build #44111 failed 9781294

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

cc @criamico

[nchaulet]

LGTM 🚀