This PR will remove the dependency on code.gitea.io/gitea/modules/structs and copy all necessary structs from that package.
After this change, we have to consider how to resolve the compatible between go-sdk and gitea.
I propose to create branches/tags on go-sdk to follow gitea’s branches/tags. That means when gitea create a new branch i.e. release/v1.10. go-sdk should also create a branch release/v1.10 to follow gitea’s change. Then you could use different branches to operate different version Gitea.