Enable a type issue property that will map to a type property in GH Issues, JIRA, etc.

$meta:
  proj: myorg/myrepo
  defaults:
    type: bug # default to 'bug' when issue has no type entry exists
issues:
  - summ: Add superpowers to API
    type: feature

Unlike tags (labels) and versions (milestones), Issuer will not create types -- they must already be present in the target issue tracker.
So no need for --auto-type nor need to add this to --auto-metadata override flag.

Release Note

A new type property of the IMYML definition structure has been added to accommodate GitHub's new issue-typing system. This change adds support for GH's GraphQL API, as that was the only way to create new issue items with type metadata.