Changelog cleanup 8.2.1 (elastic#1932)

* add 8.2.1 entry

* cleanup changelog.next

[Docs] Updated Release Notes docs for 8.2 (elastic#1895)

Cut 8.1.0 release changelog (elastic#1828)

cut 8.0.1 release changelog (elastic#1814)

Cut 8.0.0 changelog (elastic#1766)

* cut 8.0.0 release changelog

* adjust this entry

fix typo (elastic#1731)

Cutting 1.12.1 changelog (elastic#1624)

Cut 1.12 Changelog (elastic#1618)

cut 1.11 changelog (elastic#1558)

changelog entry for 1.10.0 (elastic#1445)