Bicep Application Gateway

**Issue**
During the deployment of a child resource within a parent environment, such as deploying a pre-production environment to share resources with the production environment, an observation has been made wherein the configuration of the shared Application Gateway gets replaced with the configuration of the child resources configuration.

The suggested solution involves consolidating both pre-production and production configurations into the same script to mitigate this issue. However, this approach becomes challenging when managing multiple environments, as encountered in scenarios where 3-4 environments share resources.

**To Reproduce**
Steps to reproduce the behavior:
1. Create an application gateway in Bicep with the required configuration.
2. Deploy the 'parent' resources application gateway.
3. Modify the values within the application gateway to accommodate the child environment.
4. Redeploy the application gateway, resulting in the replacement of the parent application gateway configuration with the new configuration.

**Additional context**
Efforts are aimed at avoiding reliance on additional scripting outside of Bicep.

No files, tests, or entry points are identified. Start by reproducing the four deployment steps with a parent and child Application Gateway configuration, then define behavior that preserves shared parent configuration across child deployments without external scripting.

Written by the indexing model from the issue text.