[8.16](backport #41636) [libbeat] fix: aws & openstack metadata conflict in add_cloud_metadata processor

[mergify]

Proposed commit message

This PR fixes incorrect recognition of EC2/AWS cloud provider as Openstack. The root cause was the common metadata endpoints used by both AWS SDK & Openstack logic. And this happened when IMDSv2 is disabled in AWS.

I attempted to migrate Openstack logic to another metadata implementation. However, I did not manage to create a fully functioning setup to validate the implementation. Hence, this PR focuses on a priority-based solution where priority is given for SDK-backed metadata fetching over HTTP endpoints.

Current priory providers are - aws/ec2 & azure

Note - I have done a minor refactoring to rename Local struct property to DefaultEnabled to make intention clearer

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

You need a local copy and an EC2 instance to validate the fix.

• Enable metadata service in EC2 instance and make IMDSv2 optional
• Build a beats (ex:- metricbeat) module based on this libbeat change
• Copy the beats module to EC2 instance and start the module with add_cloud_metadata processor enabled & logs set to debug for more in-depth logs & no provider enforced
• Observe logs and see data (ex:- system monitoring) through Kibana to validate cloud provider detection

Related issues

• Closes add_cloud_metadata detecting wrong cloud provider (aws as openstack) #13816

Screenshots

-IMDSv2 disabled

• Processor enabled but no provider enforced

• Debug logs on multi-result and priority based selection

• Cloud provider detected correctly,

---

This is an automatic backport of pull request #41636 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 6d4e641 has failed:

On branch mergify/bp/8.16/pr-41636
Your branch is up to date with 'origin/8.16'.

You are currently cherry-picking commit 6d4e64159b.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   CHANGELOG.next.asciidoc
	modified:   libbeat/processors/add_cloud_metadata/docs/add_cloud_metadata.asciidoc
	modified:   libbeat/processors/add_cloud_metadata/provider_alibaba_cloud.go
	modified:   libbeat/processors/add_cloud_metadata/provider_aws_ec2.go
	modified:   libbeat/processors/add_cloud_metadata/provider_azure_vm.go
	modified:   libbeat/processors/add_cloud_metadata/provider_digital_ocean.go
	modified:   libbeat/processors/add_cloud_metadata/provider_google_gce.go
	modified:   libbeat/processors/add_cloud_metadata/provider_hetzner_cloud.go
	modified:   libbeat/processors/add_cloud_metadata/provider_openstack_nova.go
	modified:   libbeat/processors/add_cloud_metadata/provider_tencent_cloud.go
	modified:   libbeat/processors/add_cloud_metadata/providers_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   libbeat/processors/add_cloud_metadata/providers.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[elasticmachine]

Pinging @elastic/obs-ds-hosted-services (Team:obs-ds-hosted-services)