Ogr

- We have implemented the closed_by property for the Pagure pull request for getting the login of the account that closed the pull request. (718)

- When using Tokman as GitHub authentication mechanism, ogr will now raise GithubAppNotInstalledError instead of failing with generic GithubAPIException when app providing tokens is not installed on the repository.
- Use the standard library instead of setuptools for getting the version on Python 3.8+,
or a smaller package on older Pythons.
This also fixes the packaging issue with missing `pkg_resources`.

- ogr now correctly raises `OgrException` when given invalid URL to
`PagureService.get_project_from_url`. (705)
- We have fixed a bug in ogr that caused `IssueTrackerDisabled` being raised
only when trying to create an issue on git project with disabled issue
tracker. Now it is also raised when getting a specific issue or
an issue list. (703)

- We have added a new optional parameter, `namespace`, to the `fork_create` method on Git projects, which allows you to
fork a project into a specific namespace. (Forking to namespaces is not allowed on Pagure.) (685)
- We have implemented a `get_contributors` function that can be used to get the contributors of a GitHub
(set of logins) and GitLab (set of authors) project. (692)
- We have introduced a new exception class `GitForgeInternalError` that indicates a failure that happened within the forge
(indicated via 50x status code). `\*APIException` have been given a new superclass `APIException` that provides status
code from forge (in case of error, invalid operation, etc.). (690)
- We have added a new property to git projects, `has_issues`, that indicates whether project has enabled issues or not.
Following up on the property, `create_issue` now raises `IssueTrackerDisabled` when the project doesn't have issues
enabled. (684)

- `Release` class has been reworked and `create_release` has been made part of the API for `GitProject`. (670)
- Factory method for acquiring project or service class from URL has been improved by checking just the hostname for determining the service. (682)

- We have added `target_branch_head_commit` property to the `PullRequest`
class in `ogr` that allows you to get commit hash of the HEAD of the
target branch (i.e. base, where the changes are merged to).