Add a way to force push from the Graph

[sergeibbb]

The graph doesn't have "Push" button that is presented in other Git UI products:

Here what we have in GitLens Graph:

User needs to Pull first. After you pull it will be a push button.

But in some cases user doesn't want to pull. For example, it's after a rebase and a force push is needed.

To sum up, an ability to perform a force push from the Graph is desired.

[d13]

Thinking in this scenario, we make the pull a split-dropdown button and offer the force push in the dropdown.