[FIXED JENKINS-23160] Newly added module locations' / additional credentials' "Add" credential button does not work

- Also changed the width of the drop-down to be auto so that the add button is more clearly associated
- Also fixed select box alignment with add button

Note:
- Root cause was f:repeatable was neither generating a new id nor re-executing the in-line script, this fixes both in one go by using Behaviour to apply the rule thus removing the need for the id on the button