Implement action artifacts server api. This change is used for supporting https://github.com/actions/upload-artifact and https://github.com/actions/download-artifact in gitea actions. It can run sample workflow from doc https://docs.github.com/en/actions/using-workflows/storing-workflow-data-as-artifacts. The api design is inspired by https://github.com/nektos/act/blob/master/pkg/artifacts/server.go and includes some changes from gitea internal structs and methods. Actions artifacts contains two parts: - Gitea server api and storage (this pr implement basic design without some complex cases supports) - Runner communicate with gitea server api (in comming) Old pr https://github.com/go-gitea/gitea/pull/22345 is outdated after actions merged. I create new pr from main branch.  Add artifacts list in actions workflow page.
