Added explicit dependencies for service ordering

[jchancellor-ms]

Description

This PR adds explicit dependencies between the gateways and firewall resource types. This is to address intermittent failures that occur when Terraform attempts the parallel deployment of services in a VWAN hub.

Fixes #91

Type of Change

• [ ] Non-module change (e.g. CI/CD, documentation, etc.)
• [x] Azure Verified Module updates:
  • [x] Bugfix containing backwards compatible bug fixes
  • [x] Someone has opened a bug report issue, and I have included "Closes #{bug_report_issue_number}" in the PR description.
  • [ ] The bug was found by the module author, and no one has opened an issue to report it yet.
  • [ ] Feature update backwards compatible feature updates.
  • [ ] Breaking changes.
  • [x] Update to documentation

Checklist

• [x] I'm sure there are no other open Pull Requests for the same update/change
• [ ] My corresponding pipelines / checks run clean and green without any errors or warnings
• [x] I did run all pre-commit checks

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