add flavours to title

[elfkuzco]

Rationale

This PR adds flavours column to titles. When notifications are being processed and the new book's flavour is not in the list of title flavours, the book is moved to staging irrespective of the title's maturity. Consequently, books with flavour mismatch cannot be manually moved from staging to prod

This closes #294

[codecov]

Codecov Report

❌ Patch coverage is 84.21053% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.24%. Comparing base (8c6471d) to head (22a343d).
⚠️ Report is 2 commits behind head on title-metadata.

Files with missing lines	Patch %	Lines
backend/src/cms_backend/db/title.py	33.33%	1 Missing and 1 partial ⚠️
backend/src/cms_backend/api/main.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           title-metadata     #305   +/-   ##
===============================================
  Coverage           82.24%   82.24%           
===============================================
  Files                  58       58           
  Lines                2721     2738   +17     
  Branches              277      280    +3     
===============================================
+ Hits                 2238     2252   +14     
- Misses                410      412    +2     
- Partials               73       74    +1     

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[benoit74]

Few minor changes + we need a maintenance script to populate title flavours from existing book flavours.

[elfkuzco]

Few minor changes + we need a maintenance script to populate title flavours from existing book flavours.

Will the title flavours be made of the set of all flavours it's book has? On local, I notice there are flavours like _maxi and maxi. I figured the first might be a mistake.

[elfkuzco]

Added a maint-script that doesn't just set the title flavours from the set of it's book's flavours. It also fixes those books too whose flavours start with _. So, _maxi becomes maxi , etc