Expose DORA 4 data through GraphQL
### Background
We've recently added API support for two DORA 4 metrics: deployment frequency and lead time: https://docs.gitlab.com/ee/api/dora/metrics.html
### Release notes
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Users should be able to programmatically access DORA 4 data through both the REST API and the GraphQL endpoint.
This feature is ~"GitLab Ultimate".
### Proposal
Expose the DORA 4 data ([already available through the REST API](https://docs.gitlab.com/ee/api/dora/metrics.html)) through the GraphQL endpoint.
issue