Port PR from PBS-Java: Always Return Bid Exp

[cross-repo-issue-creation[bot]]

A PR was merged over on PBS-Java

• https://github.com/prebid/prebid-server-java/pull/3213
• timestamp: 2024-06-19T11:14:41Z

This was a bug in PBS-Java where ORTB exp was cleared if the bid was not cached server-side. It shouldn't be cleared because it can be cached client-side as well.

[bretg]

We found that PBS-Java was not returning the ORTB exp field when a bid was not cached.