## Is your feature request related to a problem?

You can currently install plugins from Github and NPM sources, but not GitLab

## Describe the solution you'd like

Copy a GitLab URL to install a plugin

## Describe alternatives you've considered

Using the plugin source editor.

## Additional context

Came from a conversation in the Users' slack

#### *Thank you* for your feature request – we love each and every one!

posthog/plugins/test/test_utils.py
import base64
from unittest import mock
from posthog.plugins.utils import download_plugin_archive, get_json_from_archive, parse_url
from posthog.test.base import BaseTest
from .mock import mocked_plugin_requests_get
from .plugin_archives import HELLO_WORLD_PLUGIN_GITHUB_ZIP, HELLO_WORLD_PLUGIN_NPM_TGZ
@mock.patch("requests.get", side_effect=mocked_plugin_requests_get)
class TestPluginsUtils(BaseTest):