fix(routing/posts): updated slug to match all subdirs

[hamzab-01]

What kind of changes does this PR include?

• Changes with larger consequences (logic, library updates, etc.)

Description

• currently, content/posts are only matched on the first level
• updated slug to match file paths of any depth, for better organisation and flexibility

  
  content/
  ├─ posts/
  │  ├─ 2024/
  │  │  ├─ third-post.md
  │  │  ├─ fourth-post/
  │  │  │  ├─ index.md
  │  │  │  ├─ picture.png
  │  ├─ 2023/
  │  │  ├─ second-post.md
  │  ├─ archive/
  │  │  ├─ first-post.md
  │  ├─ drafts/
  │  │  ├─ fifth-post.md

 - useful for i18n, can filter by language #42 

content/ ├─ posts/ │ ├─ en/ │ │ ├─ example.md │ ├─ de/ │ │ ├─ example.md │ ├─ fr/ │ │ ├─ example.md

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[chrismwilliams]

Thanks @hamzab-01 for doing this, and the descrption!