Fix/hcl templates

[msharma24]

I have made the following fixes and improvements to secure-firewall Terraform IAC.

AWS_Workshop/AWS_Workshop_Code/Resources

1. Remove the template_file as Hashicorp has deprecated it- I have implemented the templatefile() Function
2. I have also removed the hardcoded Ubuntu 20 AMI IDs from apps.tf and bastion.tf as the hardcoded AMI ids makes it hard to deploy and test in different regions of AWS. I have implemented the data resource to lookup the Ubuntu AMI id .

module - Network

1. I have removed the template_file resource and implemented thetemplatefile() Function

I have deployed and tested the AWS_Workshop_Code - it works as expected.