Refactor repository structure to include translations

[simonsan]

Fixes #345

Output can be seen here: https://simonsan.github.io/patterns

Resources:

• mdbook i8n helpers: https://github.com/google/mdbook-i18n-helpers
• Repository structure https://github.com/google/comprehensive-rust

Todo:

• [x] Elaborate on how to add a translation
• [x] check if initial rendered html state without any translation is the same as our normal book page (besides maybe the top right globe containing only English)

[simonsan]

All checks run through, I still need to test for the output and usability.

[simonsan]

Ready to review, we need a few changes after merge:

• deploying to pages from GH action: https://github.com/rust-unofficial/patterns/settings/pages
• change environment protection rules for github-pages to be able to push from main: https://github.com/rust-unofficial/patterns/settings/environments/89922935/edit

[simonsan]

These actions have been removed and replaced:

Markdownlint, has been replaced with dprint as dprint can also format code within md files.

[simonsan]

@MarcoIeni Reverted the change I made and updated messages.pot :D Need to review again :/