Incoming webhooks don't return post id

Hello,

When creating a post using an incoming webhook, the post id of the newly created message isn't returned in any way. That makes the application which used the webhook unable to interact with this post later on.

This is for example an issue in Matterbridge that needs to know the ID of the messages it send in order to correctly format replies made on mattermost before sending them on other platforms.

I'm also noticing that there are no webhook api endpoint is not able to post messages in threads. Webhooks also can't edit or delete a previously made post (something comparable to https://discord.com/developers/docs/resources/webhook#edit-webhook-message or https://discord.com/developers/docs/resources/webhook#delete-webhook-message in the discord api). But maybe this is a separate issue about overall improvements around the features of the webhooks APIs