feat: add reactiongroups in `MessageResponse`

[guerinoni]

CLA

• [x] I have signed the Stream CLA (required).
• [ ] Code changes are tested

Description of the changes, What, Why and How?

This adds new field in MessageResponse that represents a map of reactions for that msg. As a key you have the type ('like', 'love') and as value some useful information for building a better UI.

[github-actions[bot]]

Size Change: 0 B

Total Size: 367 kB

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `dist/browser.es.js` | 79.2 kB | | `dist/browser.full-bundle.min.js` | 48 kB | | `dist/browser.js` | 80.3 kB | | `dist/index.es.js` | 79.3 kB | | `dist/index.js` | 80.3 kB |

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