PCluster expects to execute scripts out of /tmp

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## Bug description

Provide the following information:
- A clear and concise description of the bug and its impact on ParallelCluster customers
- Steps to reproduce the bug, including an example configuration file
- Versions of the various components (CLI package, node daemons, cookbook, etc.) affected by the bug
- Workaround customers can use until a fix is in place, or the fix itself if it's already done

Due to security concerns, all of our corporate AMIs do not allow script execution from /tmp.
Thus, create and createami commands fail.
As a workaround for create, I download and update yaml templates files to update user data sections for master and fleet servers.
I also have to download and update the main json stack file to point to my new Master server sub-stack file.
I also have to use the undocumented config parameter hit-template to point to my local fleet substack file

Would it be possible to have a config options to point to bash scripts to add to the beginning of user data sections of master server and fleet substacks?
Then, I could easily add commands to remount /tmp to allow execute and add environment variables to fix SSL trust issues.