Create tags for nested go modules as part of the release

[scothis]

When creating a release of cartographer-conventions, we need to create a tag. Part of the release is the webhook library that is a nested go modules. In order for go to resolve the nested module, we need to define an additional tag prefixed with the path of the modules. For a v0.0.0 tag, we also need to tag webhook/v0.0.0 for the same commit.

Currently, we create these tags manually, but it's annoying and there's always a chance we miss the step. Instead, we should create the extra tag in the release stage of CI. With #62 we no longer run CI for non-semver tags, so there's no risk of creating an infinite loop.