feat: add board section and word models

[jsgalarraga]

Description

Added the models to store the crossword board in the database:

• BoardSection model
• Word model

The sizes of the board sections are not yet determined and will be adjusted to have a good balance between

1. having a lot of sections with a few words which might be better for rendering since you only get the words that are going to be shown
2. having less sections with more words, which optimizes db reads. With this alternative, all the words fetched might not be rendered and the client will have to decide which does it render

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore