Update CHANGELOG.md for 9.1.4

CHANGELOG.md

...247-emails-forwarded-to-service-desk-email-don-t-come.yml

...nreleased/30973-network-graph-sorted-by-date-and-topo.yml

...rigger--causes-http-500-when-accessing-settings-ci_cd.yml

changelogs/unreleased/31978-cross-reference-fix.yml

...ased/dont-blow-up-when-email-has-no-references-header.yml

...elogs/unreleased/fix-import-export-missing-attributes.yml

changelogs/unreleased/fix-search-not-highlighting.yml

changelogs/unreleased/merge-request-poll-json-endpoint.yml