Cloud Slack Documentation

[huseyinbabal]

Description

Changes proposed in this pull request:

• Restructured slack related docs
• Added cloud slack howto
• Added cloud socket slack how to

Testing

Related issue(s)

Relates https://github.com/kubeshop/botkube/issues/865

[huseyinbabal]

@pkosiec added extra section for cloud commands with supportive screenshots. and cloned the slack installation process into cloud doc.