[Module Proposal]: `avm-ptn-openai-cognitivesearch`

### Check for previous/existing GitHub issues/module proposals

- [X] I have checked for previous/existing GitHub issues/module proposals.

### Check this module doesn't already exist in the module indexes

- [X] I have checked for that this module doesn't already exist in the module indexes.

### Bicep or Terraform?

Terraform

### Module Classification?

Pattern Module

### Module Name

avm-ptn-openai-cognitivesearch

### Module Details

This is a pattern module proposal for a Corporate Line of Business (LoB) ChatBot application using Azure OpenAI and Azure Cognitive Search Service. It includes:

- Azure App Gateway
- Azure App Service Premium v3 (Linux): Web App + API App
- Azure BLOB Storage
- Azure SQL Database
- Azure Cache for REDIS
- Azure App Insights
- Private VNET

*Note* This is taking over from https://github.com/Azure/Azure-Verified-Modules/issues/1000

### Do you want to be the owner of this module?

Yes

### Module Owner's GitHub Username (handle)

mikestiers

### (Optional) Secondary Module Owner's GitHub Username (handle)

andbron