Updated CI min limit timeline for Public Projects in Customer FAQ

Why is this change being made?

Due to the recent CI min limit announcement, many people with public projects, especially large open source projects using the Free tier, are worried about the upcoming changes and how they will be affected.

Right now, CI mins are not being counted for public projects on Free, which essentially means that they are using unlimited CI.

Samba and other open source projects have voiced serious concerns about seeing a big reduction in CI, especially since the GitLab for Open Source program does not necessarily fit their needs (not enough CI mins and trouble with an individual assuming liability of an entire project). See forum thread about this here: https://forum.gitlab.com/t/ci-cd-minutes-for-free-tier/40241/

This FAQ update acknowledges that the bug means that public projects will not see a change in CI minutes, and that we will make an additional announcement and provide at least 8 weeks notice, as per @kencjohnston's comment in the bug: gitlab-org/gitlab#243722 (comment 416630076)

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
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  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.