Generate github release notes from changelog + tags

[silesky]

Given the git tags and the changelog, create github releases (https://github.com/segmentio/analytics-next/releases) with the appropriate release notes.

This has some unit tests, and was also tested on a "test" repo.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 890efcc

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[zikaari]

Sick!