Send reason of WebSocket close by server

[evdokimovs]

Part of #27

Required for #33 and #55

Synopsis

We need to send reason of WebSocket closing by server to client.

Solution

• 1. Add reasons to medea-client-api-proto
• 2. Send this reasons from Medea on WebSocket close

Checklist

• Created PR:
  • In draft mode
  • Name contains WIP: prefix
  • Name contains issue reference
  • Has k:: labels applied
  • Has assignee
• Documentation is updated (if required)
• Tests are updated (if required)
• Changes conform code style
• CHANGELOG entry is added (if required)
• FCM (final commit message) is posted
  • and approved
• Review is completed and changes are approved
• Before merge:
  • Milestone is set
  • PR's name and description are correct and up-to-date
  • WIP: prefix is removed
  • All temporary labels are removed

[evdokimovs]

FCM

Send reason of WebSocket close by server (#58)

- add CloseDescription and CloseReason to 'medea-client-api-proto' crate
- send CloseDescription when closing WebSocket connection on Medea side