Update Slack API dependency and remove workaround for stripping event details from logs

[pkosiec]

ISSUE TYPE

• Feature Pull Request
• Bug fix Pull Request
• Docs Pull Request

SUMMARY

⚠️ NOTE: For convienence, this PR depends on #603 and needs to be rebased when #603 is merged (it should happen very soon). Actual changes: a6d91f2

As the upstream fix has been merged (slack-go/slack#1067), this PR updates slack-go/slack dependency and removes no longer needed workaround.

See the original issue: #579
See the PR that introduced the workaround: #583

TESTING

NOTE: You can also use pkosiec/botkube:rm-slack-workaround Docker image for testing. The image was repushed after rebase.

1. Checkout this PR
2. Edit comm_config.yaml and enable Slack
3. Export needed envs:

export KUBECONFIG=/Users/$USER/.kube/config
export LOG_LEVEL=info

4. Run BotKube locally:

go run ./cmd/botkube/main.go

5. Start Slack huddle and say something, then leave
6. Observe logs still without event details

[mszostok]

tested, works as expected 👍