Add `IPostContainerManager#setTopic`

[freya022]

Pull Request Etiquette

• [X] I have checked the PRs for upcoming features/bug fixes.
• [X] I have read the contributing guidelines.

Changes

• [ ] Internal code
• [X] Library interface (affecting end-user code)
• [X] Documentation
• [ ] Other: _____

Closes Issue: NaN

Description

Add missing setTopic in post container managers