Default evidence collection flag to on

What does this MR do?

Based on the discussion in !22855 (comment 271388833), it seems all the reasons for defaulting the flag off have been taken care of. I've turned it on in staging and dev and all appears well. Let's default it on.

You can see a release with evidence collection at: https://dev.gitlab.org/sarahghp/evidence-collection-ff-test/-/releases

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry -> was added in !18874 (merged)
• Documentation -> see !22855 (merged)
• Code review guidelines
• Merge request performance guidelines
• Style guides

Availability and Testing

• Review and add/update tests for this feature/bug. -> FE tests in added in !18874 (merged), BE tests in related BE MRs