Add an aggregate stats to the plugin manager's view

[Xpirix]

• This PR is for the issue #39

Changes summary

• Add GeoIp to the project
• Add country_code and country_name to the model PluginVersionDownload. For existing records, the values of these fields are set to N/D (not determined)
• Create or update the record when a download request has been made
• Add a Stats tab in the plugin details page: Map of downloads per country and top download per country

Requirements

• This feature needs Metabase. There are already some open PRs that implement Metabase: #274 or #310
• Generate the dashboard in Metabase
• Add the dashboard URL to the environment variables (METABASE_DASHBOARD_URL)

Please find below a GIF for this feature:

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (6589e3c) 81.94% compared to head (5bd44bc) 82.05%.

Files	Patch %	Lines
qgis-app/plugins/utils.py	83.33%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #331 +/- ## ========================================== + Coverage 81.94% 82.05% +0.11% ========================================== Files 139 140 +1 Lines 5418 5457 +39 ========================================== + Hits 4440 4478 +38 - Misses 978 979 +1 ```

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[dimasciput]

@Xpirix please fix the conflicts