add region to database

[elfkuzco]

Rationale

Add Region table for keeping information of countries and mirror location. In order to keep the data in the db compatible with the schema changes, the region data for Country and Mirror are set to None by default. However, CLI commands which update mirrors and countries update this field accordingly.

To synchronize the data in the db fully, one should create the regions first using mirrors-qa-backend create-countries < csv-file. Afterwards, mirrors-qa-backend update-mirrors. This updates the region data for all the mirrors in the database.

This resolves #38

Changes

• add region model to database
• add region relationship to country table
• add region relationship to mirrors table. This would simplify db queries while generating mirrorbrain config on metabase
• add cli subcommand that fills the region table and updates the list of countries from csv file. Run mirrors-qa-backend create-countries -h to see the arguments
• update mirror country information via update-mirrors subcommand

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 73.62637% with 24 lines in your changes missing coverage. Please review.

Project coverage is 72.75%. Comparing base (95c2609) to head (edd6bb4). Report is 4 commits behind head on main.

Files	Patch %	Lines
backend/src/mirrors_qa_backend/entrypoint.py	0.00%	12 Missing :warning:
backend/src/mirrors_qa_backend/db/mirrors.py	66.66%	2 Missing and 3 partials :warning:
backend/src/mirrors_qa_backend/cli/country.py	88.00%	1 Missing and 2 partials :warning:
backend/src/mirrors_qa_backend/db/region.py	81.25%	2 Missing and 1 partial :warning:
backend/src/mirrors_qa_backend/extract.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #42 +/- ## ========================================== - Coverage 72.83% 72.75% -0.08% ========================================== Files 28 30 +2 Lines 795 881 +86 Branches 70 81 +11 ========================================== + Hits 579 641 +62 - Misses 204 222 +18 - Partials 12 18 +6 ```

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