Slack slash integration - add ability to turn off attachment in response message for new issue creation

Proposal

Currently, the slack slash integration for creating a new issue ( /gitlab project-alias issue new title description ) gives a response that creates a lot of noise in slack channels, with no benefit.

Referring to the screenshot below, as the feature currently stands, the four fields displayed in the issue overview section (I refer to this as a summary after this) will always be None as these fields cannot yet be set using the slash command. The only useful part of this summary section is the link to the new issue. If the text in the preceding line were instead changed to make the Issue number a clickable link (as seen in the 2nd image below), the summary becomes redundant - and reduces noise in slack channels!

The preferred output for creating new issues would appear as follows:

This proposes creating the ability to toggle OFF the summary for the slash command used for creating new issues. This would be editable in the settings for the integration in the project along with setting the project alias for the integration. The behavior can remain the same as it currently is by default, but with the added choice to disable the summary for new issues.