Use description of a PR

[OpenCode]

There are cases where the text of the changelog needs to be particularly articulate. For example you need to add pieces of code, links, etc.

In such cases, it would be useful to be able to have in the configurations the option to use the PR description as a section of the changelog instead of its title.
A key could be added in the configurations for cases of changelog_type = pull_request (to indicate a value between "title" or "description")