Implement check for authorized users of slash command dispatcher

[anniehedgpeth]

What problem would you like to address?

Currently for someone to run the slash commands (i.e. /test all), the user must be admin of the repo. This security posture is not preferred.

Who is the audience for this request?

TFE engineers / maintainers of this repo

What would the ideal solution look like?

Implement a conditional that is a check of authorized users for the slash command dispatcher action, like done here

What alternatives have you considered?

What we're doing now

How does this impact you?

Currently we have to add everyone as a user and remember to remove admins when they're offboarded.

Are there any deadlines?

Is there any additional context?