Fix Azure Firewall recommendation description

[tksh164]

Overview/Summary

Fixed the description of the Monitor AZFW Latency Probes metric recommendation because AZFW Latency Probe is a name of the metric. We should use the correct metric name.

https://learn.microsoft.com/en-us/azure/well-architected/service-guides/azure-firewall

Related Issues/Work Items

None

Breaking Changes

1. Fixes the description of the Monitor AZFW Latency Probes metric recommendation.

As part of this pull request I have

• [x] Read the Contribution Guide and ensured this PR is compliant with the guide
• [x] Checked for duplicate Pull Requests
• [x] Associated it with relevant GitHub Issues or ADO Work Items (Internal Only)
• [x] Ensured my code/branch is up-to-date with the latest changes in the main branch
• [ ] Ensured PR tests are passing
• [x] Performed testing and provided evidence (e.g. screenshot of output) for any changes associated to ARG queries
  • Tested by hugo server on my local machine.
• [x] Updated relevant and associated documentation (e.g. Contribution Guide, Docs etc.)

[ejhenry]

@Azure/aprl-networking please review