Import releases from Gitea
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### Context
Right now, the Gitea importer does not attempt to import releases [citing](https://gitlab.com/gitlab-org/gitlab/-/blob/488474-combined-ultimate-duo-ent-trial-widget/lib/gitlab/legacy_github_import/importer.rb?blame=0#L63) an [issue on Gitea](https://github.com/go-gitea/gitea/issues/330) that has since been completed. Gitea has now had an API for releases since 2017.
### Proposed Solution
Remove [the logic that skips `import_releases` for gitea imports](https://gitlab.com/gitlab-org/gitlab/-/blob/488474-combined-ultimate-duo-ent-trial-widget/lib/gitlab/legacy_github_import/importer.rb?blame=0#L68), verify and make any changes necessary to support Gitea's API, and update specs to reflect Gitea's API response.
issue