Provide customActiveChannel prop for ChannelList

**Motivation**
React SDK has the ability to set active channels when we navigate to ChannelList which is useful if we wanna highlight a target channel. React Native SDK does not have it as I see.

**Proposed solution**
Provide 'customActiveChannel' property.

**Acceptance Criteria**
The user is able to see some channels as active when they navigate to ChatList.
