[8.17](backport #42746) [meraki] fix panic due to uninitialized device wifi structs

[mergify]

Overview

This PR fixes a panic occurring when fetching device channel utilization data by ensuring proper initialization of wifi0 and wifi1 struct pointers before access. It also replaces *meraki.Client with an interface to facilitate testing.

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.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes [meraki] panic due to uninitialized device wifi structs #42745

Use cases

Screenshots

Logs

---

This is an automatic backport of pull request #42746 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of cd883f5 has failed:

On branch mergify/bp/8.17/pr-42746
Your branch is up to date with 'origin/8.17'.

You are currently cherry-picking commit cd883f511.
  (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:   x-pack/metricbeat/module/meraki/device_health/device_health.go
	modified:   x-pack/metricbeat/module/meraki/device_health/device_health_test.go
	modified:   x-pack/metricbeat/module/meraki/device_health/devices.go
	modified:   x-pack/metricbeat/module/meraki/device_health/switchports.go
	modified:   x-pack/metricbeat/module/meraki/device_health/uplinks.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   NOTICE.txt
	both modified:   go.mod

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/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)