Mattermost-server: Allow plugins trigger interactive dialogs even without clicking an interactive button/menu or using a slash command

[esethna]

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Notes: Jira ticket

Currently, the OpenDialogRequest to trigger an interactive dialog requires a TriggerId, which is generated when the dialog is opened via an interactive button, menu or a slash command.

When a plugin triggers an interactive dialog outside of these three user actions, the TriggerId does not get generated and as a result, the dialog doesn't open.

This prevents certain use cases for plugins, such as when a user triggers a dialog via Main Menu item described here.

Proposed change: Allow plugins to trigger interactive dialogs even when the TriggerId is empty.

[scottleedavis]

If/when this is up for grabs I'd be interested. (unless this is for someone else, that is ok. :)

[hanzei]

Surely, go ahead @scottleedavis. Glad, you are looking into this!