Migrate legacy Slack tests to Cloud Slack

[pkosiec]

Description

This is a follow-up of #631. Slack App directory will unapprove our legacy Slack app on December 21st. It means that users will see a warning or be blocked from installing it, if not allowed with their workspace settings

• Remove legacy Slack docs from docs.botkube.io and add deprecation notice - in Deprecate legacy Slack integration and fix replacing MS Teams version metadata botkube-docs#178

• Remove configuration and logic for legacy Slack Extracted here

• For Cloud: @huseyinbabal https://github.com/kubeshop/botkube-cloud/pull/560

  • add scopes column to API key database
  • manually create API key not connected to any deployment for test user (on Cloud Dev)
  • ensure it gets the custom scopes than deployment-related API key (in api key middleware)
  • use this API key to authenticate to Botkube Dev GraphQL API

• Migrate E2E tests to Cloud Slack to make them able to run on CI: @huseyinbabal Cloud Slack E2e Tests #1205

  • We need to make sure the Cloud account have subscription enabled with Cloud Slack quota
  • Make sure this test can be run in parallel (we will still run it on PRs and main branch)
  • Rework some assertions
  • Move E2E RBAC and other configuration to cloud so that the test assertions work properly

• Once all other items are finished, try to refactor Cloud Slack and Socket Slack to share same logic (so that it is tested with the tests) Extracted here

Blocked by

#1261