Retention - Input field when creating a rule should be optional

Using LTS 2021

• Install nuxeo-retention addon
• Login as an administrator
• Go to retention menu, rules
• Create a rule
• Select based on an event

=> Input field is mandatory

Expected: field should be optional as mentioned in the comment of NXP-28899

Reasons

• This field was made mandatory initially as it was expected to take an EL expression. Scope was changed (event based rules only accept hardcoded values at this stage) but UI was not updated to match.
• If the event is generic (e.g. the default values of document moved or document modified), no input will be sent and the rule cannot be leveraged. If the field is optional, it is for example possible to assign the rule to the document and move the document afterwards in a dedicated location, which will trigger the start of the retention.
• As confirmed in NXP-28899, this field was supposed to be optional