FR: Add support for custom set time and sender attribute

### Description

Hey everyone,

we are using your Chat Component for a project in nodered and would like to be able to load an already saved chat back into the component, but we are currently facing the problem that all messages get set to the current timestamp and sent gets set to false.

I would like to create a FR and implement it.
My Time estimate for the change is 10-15mins

The issue names no files or tests. Start by locating the Chat Component entry point and the message handling that assigns timestamps and sender state; done means loaded messages can retain supplied time and sender values, with the relevant behavior covered by the project's existing tests.

Written by the indexing model from the issue text.