Remove automatic fill option for default Wi-Fi Overview dashboard

[iglendd]

What does this PR do?

Add .fill(null) to many widgets of the default Wi-Fi Overview dashboard

Motivation

If fill option, which is default behavior, is not removed then Wi-Fi drop are not shown or visible or discernable in the graph, and it defeat the main goal of the dashboard - Wi-Fi troubleshooting which should report Wi-Fi drop.

Review checklist (to be filled by reviewers)

• Add your own Windows machine to an org
• Disable Wi-Fi for a few minutes
• Reenable Wi-Fi
• Go to the org Wi-Fi Overview and see the drop in its widgets.

• [ ] Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• [ ] Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• [ ] If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[github-actions[bot]]

⚠️ Recommendation: Add qa/skip-qa label

This PR does not modify any files shipped with the agent.

To help streamline the release process, please consider adding the qa/skip-qa label if these changes do not require QA testing.