Update CHANGELOG.md for 8.16.0

changelogs/unreleased/badge-color-on-white-bg.yml

changelogs/unreleased/bug-project-feature-compatibility.yml

changelogs/unreleased/clipboard-button-text.yml

changelogs/unreleased/didemacet-ci-lint-page.yml

changelogs/unreleased/dot-in-project-queries.yml

changelogs/unreleased/dz-nested-group-misc.yml

changelogs/unreleased/dz-rename-invalid-users.yml

changelogs/unreleased/env-var-in-redis-config.yml

...nreleased/feature-1376-allow-write-access-deploy-keys.yml

...gs/unreleased/feature-admin-merge-groups-and-projects.yml

changelogs/unreleased/feature-gitaly-feature-flag.yml

...gelogs/unreleased/feature-log-ldap-to-application-log.yml

changelogs/unreleased/feature-more-storage-statistics.yml

changelogs/unreleased/filename-to-file-path.yml

changelogs/unreleased/fill-authorized-projects.yml

changelogs/unreleased/fix-api-deprecation.yml

changelogs/unreleased/fix-blame-500.yml

changelogs/unreleased/fix-boards-search-typo.yml

changelogs/unreleased/fix-broken-url-on-group-avatar.yml

changelogs/unreleased/fix-build-sort-order.yml