Pull from upstream for non git upstreams (or no upstreams at all)

[majamassarini]

Description

We want to be able to call the pull-from-upstream procedure without a git upstream or without a git upstream at all.

#2136 is a draft PR example we want to improve with a better refactoring. This card is a follow-up for #2099

Pull from upstream needs to call actions in the Upstream object. The Upstream object inherits from the PackitRepositoryBase.

We need a new kind of Upstream object, suppose to name this new object NonGitUpstream. We need to reuse from the PackitRepositoryBase the action handler related code.

1. [x] #2287
2. [ ] Reuse the same ActionManager/Handler in the new NonGitUpstream and in the old Upstream
3. [ ] The new NonGitUpstream should share the same interface with the old Upstream but different implementations for everything is accessing a git repo. It should not depend on PackitRepositoryBase.
4. [ ] Make the sync_downstream method use the new NonGitUpstream when no upstream_project_url is given for a pull-from-upstream invocation
5. [ ] Adjust things also for packit-service