Updating Slack engine to use slack_bolt

[garethgreenaway]

What does this PR do?

Updating Slack engine to use slack_bolt

What issues does this PR fix or reference?

Fixes: #57842
Fixes: #62812

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

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Yes

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[Ch3LL]

This looks to be a breaking change for users using the slackclient as it will require them to install a dependency and update their configs to include app_token and bot_token. Is there a reason we are not including the old slackclient functionality and putting it on a deprecation path?

[joshperry]

I think @Ch3LL is right here. The rtm API still works with slack and I just set up a "legacy bot user" which is able to successfully send messages from our v3004 install. It'd be nice to have a deprecation path for this so that our integration doesn't stop working immediately when we upgrade to v3006 with no way to smoothly transition.

It's also important to note that while Slack does recommend moving away from the rtm API, they have not deprecated it.

https://slack.dev/node-slack-sdk/rtm-api

RTM isn’t available for modern scoped apps anymore. We recommend using the Events API and Web API instead. If you need to use RTM (possibly due to corporate firewall limitations), you can do so by creating a legacy scoped app. If you have an existing RTM app, do not update its scopes as it will be updated to a modern scoped app and stop working with RTM.

Once you create a legacy scoped app, you just need to add the Bots feature, and when the app is installed you'll be given a bot token, which is what I put in the as the api key in our salt config.

On the permissions page for the app, there will be a warning recommending to update to granular scopes:

However, as the warning at the top of the scope update page says, the app will no longer be able to use the rtm API if you change to granular scopes: