Refactor chat bot enabled checks

What does this MR do and why?

Related to https://gitlab.com/gitlab-org/enablement-section/tanuki-bot/-/issues/25 and https://gitlab.com/gitlab-org/gitlab/-/issues/408976

This MR does a few refactors related to when the GitLab chat is available:

• refactors allchecks into one shared method and removes the helper (and it's spec)
• change the plan used to check if the feature is available to use all saas plans that should have the feature enabled (was just ultimate, but now includes ultimate, ultimate trial, open source, and gold plans)

Screenshots or screen recordings

N/A

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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