Feat 118 message spacing

[jreamy]

This addresses https://github.com/TryQuiet/quiet/issues/188 to insert larger line breaks between grouped messages.

Pull Request Checklist

• [x] I have linked this PR to a related GitHub issue.
• [x] I have added a description of the change (and Github issue number, if any) to the root CHANGELOG.md.

[jreamy]

Two few questions @holmesworcester:

1. Do you think this is a good approach? I thought about just inserting a
   or other divider between each <NestedMessageContent>... thoughts on which approach you would prefer?
2. How much spacing do you want here? I started with 7 pixels, but it could be more... in #1403 you said 1.5 lines which would be ~10 px margin

7px margin:

10px margin:

[holmesworcester]

That approach with 10px looks good to me!