added new metric category facet type - #39573

• All applicable files are owned properly
  _{Digest: 1c7f51d}
• There are 1 of 1 commits unsigned in this pull request. Existing unsigned commits will need to be amended or rebased.
  Unsigned commits: b2f7c32 In the future, it will block merging.
  _{To fix please use sign-pull-request https://github.com/DataDog/documentation/pull/39573 tool - more info on Confluence. Otherwise, make sure you're configured to sign commits by default, check out our documentation for help. If you need support, contact us in #git. Questions about this check? Reach out in #devflow on Slack.
  Digest: 950d0c0}
• All required reviewers have approved
  _{Digest: d8ce28d}

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