[PARENT] Design Notes should also be available in the discussions tab

• Backend weight: 3
• Frontend weight: 2

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Problem to solve

When discussions take place in the Design tab of an issue or merge request those conversations are siloed to the design tab. This prevents other users from seeing the complete discussion within a single tab of the merge request.

Further details

We already support this behavior for other types of discussion (i.e. comments on specific lines of code during a merge request), and those conversations are surfaced in the main Discussions tab of the merge request.

Proposal

Proposal and mockup have been updated to what's in the description of the corresponding FE issue.

Documentation

[Please add relevant documentation changes here]

Links / references