WIP Update blog post for open source announcement with feature and tier plans

Link to review app for this post: https://cdybenko-master-patch-06133.about.gitlab-review.app/blog/2020/03/30/new-features-to-core/index.html

Why is this change being made?

Slack from @sytses: https://gitlab.slack.com/archives/C3MAZRM8W/p1585699672149500

Note from @mterhar

We haven't open sourced these features but since the intention is to provide them for free, we have updated the EE offering to reflect that for all the features except the following:

• List exceptions

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what