Add missing `x-total-count` header for pagination APIs

[pd4d10]

• Gitea version (or commit ref): v1.1.1
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant

Description

User's repo list API has a x-total-count response header to give the total count info.

Is there any plan to add it to other pagination APIs?

• https://gitea.com/api/swagger#/user/userListRepos
• https://gitea.com/api/swagger#/user/userListStarred
• https://gitea.com/api/swagger#/user/userListSubscriptions
• https://gitea.com/api/swagger#/repository/repoListStargazers
• https://gitea.com/api/swagger#/repository/repoListSubscribers

Haven't checked all APIs yet. Just find these in GitTouch's development.

Related issue: pd4d10/git-touch#106