chore: convert changelog to markdown (#5672)

* chore: move changelog to markdown

* chore: switch to simpler block def

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* style: pre-commit fixes

* chore: handle more block ends

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* docs: fix md display

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* docs: one more fix

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* style: pre-commit fixes

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Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>