[GH-1309] Correct Attachments documentation

[Omar8345]

Summary

This pull request corrects misinformation in the attachments documentation, in the end of the documentation, it instructs the developer to add an attachments key in the props field, which won't work, I have edited the documentation and the curl and HTTPS examples to add the attachments key in the top-level of the post's JSON.

Ticket Link

Fixes https://github.com/mattermost/mattermost-developer-documentation/issues/1309

[mattermost-build]

Hello @Omar8345,

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[cwarnermm]

Thanks, @Omar8345, for this developer documentation PR. Your proposed changes will be technically reviewed by Engineering.

[Omar8345]

Thanks for the PR, @Omar8345! I think there might be some confusion going on here because the syntax in those examples matches how POST /api/v4/posts expects the payload to look.

When you tried this, were you perhaps using an incoming webhook? I think the payload sent to a webhook uses the attachments field without props like in your changes.

If that's the case, I think we could instead add a separate example for posting message attachments using a webhook. If we do that, we should probably also update the existing examples to be posting to https://{your-mattermost-site}/api/v4/posts since that's the correct API endpoint for that

Thanks for your catch, I have made the corresponding changes requested and added a section for how to post a message attachment using a webhook.

[Omar8345]

Actually, would you be able to apply those? I guess I don't have the required permission to do that here

Applied your suggested edits! I was a bit confused 😅

Edit: I just made a commit because I discovered that the curl and HTTP requests in the first FAQ wasn't putting attachments key inside props field

[cwarnermm]

@Omar8345 - Can you update your branch with latest master, please? Thanks!

[Omar8345]

Done @cwarnermm

[cwarnermm]

@hmhealey - This PR is ready for your review.