[Fleet] Allow to delete orphaned agentless policies

[nchaulet]

Summary

Resolves #266426

When an agentless agent policy is manually deleted from Elasticsearch, its associated package policies become orphaned. Attempting to delete them through the agentless API fails with a 404 because the agent
policy no longer exists.

This PR handles that 404 gracefully by cleaning up orphaned resources (package policies and agentless deployment) instead of throwing.

Changes

• deleteAgentlessPolicy now catches 404 from agentPolicyService.get() and falls back to orphan cleanup instead of throwing
• deleteOrphanedAgentlessResources (new private method) deletes orphaned package policies via findAllForAgentPolicy + delete with force: true, then issues a best-effort DELETE to the Agentless API

Test plan

• Unit tests: orphan cleanup on 404, rethrow on non-404 errors
• API integration test: directly deletes the agent policy SO, then verifies the agentless delete API succeeds and cleans up the package policy

[infra-vault-gh-plugin-prod]

Pinging @elastic/fleet (Team:Fleet)

[kibanamachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 3c2b177
• Build duration: 50 mins

Metrics [docs]

✅ unchanged

History

• 💔 Build #450511 failed e0f86ad
• 💔 Build #450435 failed db5b8f6

cc @nchaulet

[MichelLosier]

Looks and works great!

[MichelLosier]

[nit] Think we can avoid the any type here

Suggested change

	private async deleteOrphanedAgentlessResources(policyId: string, user?: any) {
	private async deleteOrphanedAgentlessResources(policyId: string, user?: AuthenticatedUser, {

WIth that may not need to ?? undefined below, since the AuthenticatedUser type is expected.