Support for MatterMost without System Admin Role

[kazukifujiwara]

Environment

• Nautobot version: latest
• nautobot-plugin-chatops version: latest

Proposed Functionality

(ChatOps for MatterMost)
Optionally disable ephemeral posts to allow bot users without System Admin role to use ChatOps.

Currently bot user needs to be created as System admin role to create ephemeral posts (Mattermost constraint).
https://api.mattermost.com/#tag/posts/operation/CreatePostEphemeral

Use Case

Using ChatOps for Mattermost in environments where bot user with System Admin role cannot be created (mattermost managed by another organization).