Use rounded corners on changelog images

[gtsiolis]

Describe your feature request

Problem to solve

In the latest changelog we experimented with adding more imaged in the changelog entry.

Proposal

Using rounded corners, slightly smaller than the rounded corners used in the header image.

Using rounded-lg or rounded-xl could suffice.

User impact

Most, if not all, images on www.gitpod.io are using some radius.

Additional context

No response