[AVM Module Issue]: Various features in `avm/ptn/dev-ops/cicd-agents-and-runners` module

### Check for previous/existing GitHub issues

- [x] I have checked for previous/existing GitHub issues

### Issue Type?

Feature Request

### Module Name

avm/ptn/dev-ops/cicd-agents-and-runners

### (Optional) Module Version

_No response_

### Description

The following features would be nice to have in the module

* Possibility to configure additional environment variables on Container Instances and Container Apps resource
* Possibility to configure custom runner images
* Possibility to use existing Log Analytics Workspace
* Possibility to use existing Azure Container Registry
* Make githubRepository parameter optional (for organization scope deployment of runner)
* Add support for Managed DevOps pools: `avm/res/dev-ops-infrastructure/pool`
* Add Azure Firewall as an optional configuration to align module towards Well-Architected Framework

When networkType: 'createNew'
* (Would be nice) Use cdir function to configure subnets based on addressSpace parameter instead of hard coded subnet size as default (makes the deployment fail if subnet configuration is missing from networkConfiguration)
* Enable/disable if private DNS zones should be deployed or not.

I'd like to add features from this module proposal to the list: https://github.com/Azure/Azure-Verified-Modules/issues/1878
- Docker image creation
- Bring your own dockerfile, or use the default dockerfile
- Bring your own entrypoint shell script, or use the default entrypoint
- Rebuild the container image on a schedule, and purge old images from the container registry

### (Optional) Correlation Id

_No response_