Add craft to sentry-elixir

[AbhiPrasad]

Craft is Sentry's universal release tool. It would be nice to add it to sentry-elixir so when we do releases, we can push new versions to Sentry's release registry. This allows us to add features to our docs/product to call out new versions of sentry-elixir. Would be great to get something like below on the Elixir docs for example.

Eventually we'll need to do releases through craft, but we first need to support Hex as a target for this. Opened an issue to track that in the craft repo: getsentry/craft#409

[sl0thentr0py]

https://hex.pm/docs/publish#publishing-from-ci