feat: use current timestamp for Credly badge issuance date

[luisfelipec95]

Description

Updates the issued_at timestamp sent to Credly when issuing a badge.

Previously, issued_at was set to badge_template.created (the creation date of the badge template). This caused badges to be backdated to when the template was created rather than showing the date when the badge was actually awarded to the user.

Testing Instructions

1. Award a Credly badge to a user where the badge template was created in the past.
2. Check the issued badge details on Credly to confirm Issued on matches the current timestamp instead of the template creation date.

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