Validation for work item due date

Background

Discovered in #501693 (comment 2215288388), some work items have due dates that fails validation for Elasticsearch which prevents indexing work items for search. The dates should be validated before saving into the database. Elasticsearch expects ISO 8601 YYYY-MM-DD format.

Examples:

• Work item ID 155490741 has due date 20224-01-31
• Work item ID 151827816 has due date 99999-09-05

gitlab-com/gl-infra/production#18874 (closed) is a CR to fix these two dates to unblock a migration but it's almost certain that there will be similar cases if we don't have validation for work item due dates.

Proposal

Add validation before saving work item due dates.