Add raw blob endpoint to get objects by SHA ID (#5334)

Add raw blob endpoint to get objects by SHA ID (#5334)

* Add raw blob endpoint

This should make it possible to download raw blobs directly from
/:repo/:username/raw/blob/:sha1 URLs.

* fix: Make it work

* As an SHA-ID is no path getRefNameFromPath can't be used to verify
file specifying parameter
* added relevant change in go-gitea/git #132

Signed-off-by: Berengar W. Lehr <Berengar.Lehr@kompetenztest.de>
* Update Gopkg.lock

Can't update all vendors due to errors

Signed-off-by: Berengar W. Lehr <Berengar.Lehr@kompetenztest.de>
* style: Add Gitea copyright header

* feat: Added integration test for /repo/u/r/raw/blob

* fix: correct year in copyright header