UBERF-4632: refactor activity classes structure

[kristina-fefelova]

Contribution checklist

Brief description

Checklist

• - UI test added to added/changed functionality?
• - Screenshot is added to PR if applicable ?
• - Does a local formatting is applied (rush format)
• - Does a local svele-check is applied (rush svelte check)
• - Does a local UI tests are executed UI Testing
• - Does the code work? Check whether function and logic are correct.
• - Does Changelog.md is updated with changes?
• - Does the translations are up to date?
• - Does it well tested?
• - Tested for Chrome.
• - Tested for Safari.
• - Go through the changed code looking for typos, TODOs, commented LOCs, debugging pieces of code, etc.
• - Rebase your branch onto master and upstream branch
• - Is there any redundant or duplicate code?
• - Are required links are linked to PR?
• - Does new code is well documented ?

Related issues

A list of closed updated issues

Contributor requirements

• - Sign-off is provided. DCO
• - GPG Signature is provided. GPG

[kristina-fefelova]

1. ChatMessage moved to chunter
2. ActivityMessage, DocUpdateMessage, Reactions moved to activity
3. generateDocUpdateMessages moved to server-activity