Add support for `push_events_branch_filter` on `gitlab_project_hook` resource

Created by: RomanNess

We are using the gitlab_project_hook resource to automate the setup of web hooks. Unfortunately, the push_events_branch_filter attribute does not seem to be supported in the provider even though it can be set through the Gitlab API (https://docs.gitlab.com/ee/api/projects.html#add-project-hook).

Judging by the docs, I assume that this does also apply for the attributes confidential_issues_events, confidential_note_events and deployment_events on the gitlab_project_hook resource.

I can try to provide a PR myself if this feature is wanted and no one else feels responsible.