change slack auto update key

[jamesfkane]

Slack changed the key associated with auto updates, PR is to update the schema to reflect that change.

Slack deprecation documentation (announcement date 4/22/24): https://slack.com/help/articles/4426294050451-Slack-feature-retirements#retired-features

Slack documentation referencing the new key: https://slack.com/help/articles/11906214948755-Manage-desktop-app-configurations#mac-2

(wasn't sure where best to submit this PR, to this repo or https://github.com/Jamf-Custom-Profile-Schemas/jamf-manifests, so I did both 😉)

[talkingmoose]

Thanks @jamesfkane!

I've been lax keeping this repo up-to-date after the work Elliot Jordan put into ProfileManifestsMirror.

It automatically generates manifests for Jamf Pro whenever the manifests for ProfileCreator and iMazing Profile Editor are updated. That repo is much larger and better maintained.

See if the Slack manifest there is already updated.