Check for Template elements before deleting them in generate_yaml.py

[MichaelClifford]

We need to support the scenario where a user uses their own template yaml files to define their appwrappers. Due to this scenario, we should not presume the existence of any fields in generate_yaml.py and should check for their existence before deleting them. For example, disable_raycluster_tls(resources) will fail if a custom template does not define a volume.

https://github.com/project-codeflare/codeflare-sdk/blob/ec6c787c6bc060fccb82f9b6e0684d3dfc12e016/src/codeflare_sdk/utils/generate_yaml.py#L263C1-L283