Update CHANGELOG.md for 8.16.0

CHANGELOG.md

changelogs/unreleased/18786-go-to-a-project-order.yml

changelogs/unreleased/19086-double-newline.yml

...ails-when-using-group-and-project-names-instead-of-id.yml

...ed/19988-prevent-empty-pagination-when-list-not-empty.yml

...ased/21135-resolve-these-conflicts-link-is-too-subtle.yml

changelogs/unreleased/21698-redis-runner-last-build.yml

...gs/unreleased/22111-remove-lock-icon-on-protected-tag.yml

...-visibility-level-to-public-but-project-is-not-public.yml

...eleased/24139-production-wildcard-for-cycle-analytics.yml

...logs/unreleased/24185-legacy-ci-status-reactive-cache.yml

...on-top-of-each-other-depending-on-the-selected-filter.yml

...umps-to-wrong-position-when-clicking-a-comment-anchor.yml

changelogs/unreleased/24915_merge_slash_command.yml

...eleased/25277-milestone-counter-number-with-delimiter.yml

...25371-environments-date-created-column-is-not-labeled.yml

...make-colors-in-runner-status-more-colorblind-friendly.yml

...elogs/unreleased/25507-handle-errors-environment-list.yml

...ogs/unreleased/25580-trucate-dropdown-for-long-branch.yml

changelogs/unreleased/25678-remove-user-build.yml