Backport #8901
In investigating #7947 it has become clear that the storage component of go-git repositories needs closing.
This PR adds this Close function and adds the Close functions as necessary.
In TransferOwnership the ctx.Repo.GitRepo is closed if it is open to help prevent the risk of multiple open files.
Fixes#7947
* move create release from models to a standalone package
* fix lint
* fix comment year
* fix lint
* fix lint
* fix package import name
* fix vendor
* fix go mod
* some refactors
* fix vendor
* use go1.12 make vendor
* fix vendor