Move RoomId and Credentials to the 'medea-client-api-proto' crate (#27)

[evdokimovs]

Part of #27

Required for #147

Synopsis

In #147 we need to use RoomId and Credentials on the Jason side, so it was decided to move this newtypes from medea crate to the medea-client-api-proto.

Solution

Move RoomId to the medea-client-api-proto and use this newtype instead of old newtype.

Add Credentials newtype to the medea-client-api-proto and use it.

Checklist

• Created PR:
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[evdokimovs]

FCM

Move RoomId and Credentials to the 'medea-client-api-proto' crate (#148, #27)

- add and use Credentials newtype in 'medea' crate