Auto-generate changelog at `docs.lamin.ai/changelog`

[falexwolf]

Just like for all other Lamin products, important changes should be announced here: https://docs.lamin.ai/changelog

This action automates much of this process by keeping a changelog here: https://github.com/laminlabs/lamin-docs/blob/main/docs/changelog/soon/laminr.md

In all other Lamin repos, we use gitmoji to categorize commits. We think it makes the changelog easier to read and digest. Maybe you also want to consider using it here @rcannood @lazappi. But this isn't a requirement.

[falexwolf]

Merged to check whether it actually works!

[falexwolf]

Yes, works: https://github.com/laminlabs/lamin-docs/commit/f1e20eb27c285eaa1cd0303545929761a67567cf