Move code owners modal to Free tier

Overview

Code owners provides great value to teams, mainly by:

1. Clearly communicating who is responsible for a certain part of the codebase. This is useful to know who to reach out to in the event they have questions or need help.
2. Enabling workflows that require SMEs to review code changes before they are merged into the code base (in the form of approval rules).

Hypothesis

There are many Free tier users who may be experiencing problems that are solved by the code owners feature, however, these users may not know of its existence.

Bringing the code owners modal to the Free tier has the following benefits:

1. Bring visibility/discoverability into the feature. Users can then investigate what other value they can get from it
2. Allow users to find out "what's possible" by using this feature, namely how approval rules based on code owners information can be created. Even if users are on the Free tier, they would discover this information in-app, which makes for a good upgrade path.

Proposal

1. Show code owners modal in the Free tier

2. Optionally, show a grayed out "Merge Request Approvals" section in the project settings, offering an upgrade path for interested users.