install_flux.sh -- Prompt for the user password

Bug

Description

Prompt for the user's registry password instead of requiring it on the command line, which is a security risk. Not specifying the password just gives a help message:

➜  bigbang git:(71-update-k3d-to-latest) ✗ ./scripts/install_flux.sh -u Ben_Francis                                      
usage: install_flux.sh <arguments>
-h|--help                - print this help message and exit
-r|--registry-url        - (optional, default: registry1.dso.mil) registry url to use for flux installation
-s|--use-existing-secret - (optional) use existing private-registry secret 
-u|--registry-username   - (required) registry username to use for flux installation
-p|--registry-password   - (required) registry password to use for flux installation
-w|--wait-timeout        - (optional, default: 120) how long to wait; in seconds, for each key flux resource component

BigBang Version 2.4.1

Leads

The script should prompt the user and not echo the password. The -p option in the help function should change from "required" to "optional, prompted if no existing secret". Prompt for the username if not given.