Change in app message sound label

[404Wolf]

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• [X ] I have read the README and CONTRIBUTING documents
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Contributor checklist

• [x] My commits are rebased on the latest main branch
• [x] My commits are in nice logical chunks
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• iDevice A, iOS X.Y.Z
• iDevice B, iOS Z.Y

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Description

Change the app setting text for disabling in app message sounds to be "In-Chat Message Sounds." This change addresses a bit of inconsistency with the desktop signal app, and more transparently describes the functionality of the setting.