Improve the pull request timeline entry when adding or removing the `WIP: ` prefix

[silverwind]

Feature Description

Currently when a WIP prefix is added or removed:

• When the WIP: prefix is added a timeline entry <user> changed title from <title> to WIP <title> is added.
• When the WIP: prefix is removed a timeline entry <user> changed title from WIP: <title> to <title> is added.

Instead, we should shorten the text while also making it easier to understand:

• When the WIP: prefix is added, add a timeline entry <user> marked the pull request as work in progress.
• When the WIP: prefix is added, add a timeline entry <user> marked the pull request as ready for review.

The text needs to be added to the en-US translation.