[CHA-0] Add user_message_reminders field to ChannelType for channel type updates

[nijeesh-stream]

CLA

• I have signed the Stream CLA (required).
• The code changes follow best practices
• Code changes are tested (add some information if not applicable)

Description of the pull request

Changes

• Added user_message_reminders field to ChannelType model
• Added field to ChannelTypeCreateRequestData (for creating channel types)
• Added field to ChannelTypeUpdateRequestData (for updating channel types)

Why

The user_message_reminders flag was missing from the ChannelType model, which meant it was impossible to enable message reminders at the channel type level using ChannelType.update().

While reminders could be enabled per-channel via config_overrides, there was no way to set it as default for all channels of a specific type.

JavaScript SDK Equivalent

This now allows the Java equivalent of:

await client.updateChannelType("messaging", {
  user_message_reminders: true
});

Java Usage After Fix

ChannelType.update("messaging")
    .userMessageReminders(true)
    .request();

Testing

• Existing tests continue to pass
• Field properly serializes/deserializes with Jackson annotations