This commit adds a new script to devtools that can be used to help
identify duplicate changelog entries.
It works by identifying duplicate lines in CHANGELOG.md, and then
searching whether each one of those duplicate lines are present in a
separate text file (which can be a subset of the changelog that the user
is interested in analyzing)
No user-facing changes
Changelog-None
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
