RFC: Adding optional ids to Chat Messages

[nfcampos]

We are planning to add an optional id field to all Chat Message classes, see #17835. This will allow producers of messages (eg. Chat Models, Tool Executors, your own applications) to optionally add an id to a message. This id can then be used by your application to distinguish or dedupe messages.

Here is an example of a PR which modifies ChatOpenAI to passthrough the message id generated by OpenAI to the messages it outputs: #17837

Any questions or comments let us know!