[User story] Buttons with post categories & category filter

[alexkisielewicz]

As a user, I want to be able to click on a post category, so that I can view all posts belonging to that category on the posts page with the category filter applied.

Acceptance Criteria:

• The post categories are displayed in the UI.
• When a user clicks on a category, they are redirected to the posts page.
• The posts page is loaded with the applied filter for the selected category.
• The selected category is displayed on the posts page to indicate the active filter.
• Only posts belonging to the selected category are shown on the posts page.