Move icons to root /images directoy

Why is this change being made?

This MR duplicate all of the icons from sites/uncategorized/source/images/icons into source/images/icons. We need to duplicate the icons because:

• Only icons from within the sites/uncategorized/source/images/icons directory are visible to the inline_svg extension added with this MR. This extension is used extensively in the CMS events template. We will be modifying the inline_svg extension to work with our monorepo structure in this issue and remove duplicate icons.
• Only icons from the source/images/icons directory actually get built for production. This makes the all the SVG icons available incase the are used elsewhere in the site. This was specifically noticed with the slp-dashed-line.svg icon used on the pricing page. Slack thread.

To QA check that the icons are available in the review app.

For example, https://move-icons-to-root.about.gitlab-review.app/images/icons/slp-dashed-line.svg

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 one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • 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. (this requirement has been removed pending identification of a new DRI for the handbook)