Added `temporary_channel_id` to `create_channel`.

Added `temporary_channel_id` to `create_channel`.

By default, LDK will generate the initial temporary channel ID for you.
However, in certain cases, it's desirable to have a temporary channel ID
specified by the caller in case of any pre-negotiation that needs to
happen between peers prior to the channel open message. For example, LND
has a `FundingShim` API that allows for advanced funding flows based on
the temporary channel ID of the channel.

This patch adds support for optionally specifying the temporary channel
ID of the channel through the `create_channel` API.