DoltHub tag/release workflow and webhooks

**Is your feature request related to a problem? Please describe.**
I want to be able to trigger a CI action via webhook when creating a release, and be able to tell from the webhook that the event is a release, rather than having the CI action clone the database to check if the latest push event is tagged.

**Describe the solution you'd like**
I would like a release to be created automatically when pushing a tag to DoltHub, and webhooks to be triggered by this or manual release creation on DoltHub, and also these webhooks contain a field specifying whether the event is a release and the tag name.

Alternatively there could be separate hooks for different event types.

Tag behavior is a bit inconsistent at the moment. Currently, when I create a release on DoltHub and pull, the release is represented as a tag in the database. However, when I push new commits that are tagged to DoltHub, they don't show up as releases or in any other viewable way, e.g., in the commit log. I'm not sure why this is. `dolt push` doesn't have a `--tags` argument like `git push` does, so I would expect tags to always be pushed.