Add a "blog post" summary to Cherry Picking
Now when there are successful picks, it will add an additional comment to the preparation MR with some Markdown code to be used for a patch release blog post.
Example:
--> Adding the following comment to 13083!25963:
Successfully picked the following merge requests:
* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25814
* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25854
* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25859
* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26043
* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26055
--> Adding the following comment to 13083!25963:
The following Markdown can be added to the blog post:
```
* [Docs: Update upgrading_from_source.md for Ruby 2.5](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25814)
* [Update group policy to reflect all the requirements](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25854)
* [CE port for expanded pipelines](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25859)
* [Backports EE change for expanded pipelines](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26043)
* [Fix health checks not working behind load balancers](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26055)
```
--> Adding the following comment to 278964!9952:
Successfully picked the following merge requests:
* https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9627
* https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9899
--> Adding the following comment to 278964!9952:
The following Markdown can be added to the blog post:
```
* [Renders inline downstream & upstream pipelines](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9627)
* [Resolve "Add "No approval required" state to approval rules MR component"](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9899)
```
This is a somewhat boring half-step solution for https://gitlab.com/gitlab-org/release/framework/issues/186.