Embed GitOps basics video on YAML files docs page (#41581)

## Summary

- Embeds Fleet's ["The Basics of Fleet
GitOps"](https://www.youtube.com/watch?v=wgqI_lHnGJc) YouTube video on
the [GitOps YAML files documentation
page](https://fleetdm.com/docs/configuration/yaml-files).
- The video is placed in the introduction section, right after the
opening paragraph and before the first callout, so users see it early
when landing on the page.
- Uses the existing `<div purpose="embedded-content"><iframe>` embed
pattern consistent with other Fleet docs pages (e.g.,
`articles/queries.md`, `articles/fleetctl.md`,
`articles/vulnerability-processing.md`).

### Changes
- `docs/Configuration/yaml-files.md`: Added YouTube video embed for "The
Basics of Fleet GitOps" (`wgqI_lHnGJc`).

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Co-authored-by: kiloconnect[bot] <240665456+kiloconnect[bot]@users.noreply.github.com>

docs/Configuration/yaml-files.md

@@ -2,6 +2,10 @@
 
 Use Fleet's best practice GitOps workflow to manage your computers as code. To learn how to set up a GitOps workflow see the [Fleet GitOps repo](https://github.com/fleetdm/fleet-gitops).
 
+<div purpose="embedded-content">
+   <iframe src="https://www.youtube.com/embed/wgqI_lHnGJc" allowfullscreen></iframe>
+</div>
+
 > When changing a team's name, you must first change it in the UI and then update your YAML. If you only update your YAML, the team will be deleted and the team's hosts will lose their settings. This happens because the hosts are transferred to "No team".
 
 Any settings not defined in your YAML files (including missing or misspelled keys) will be reset to the default values or deleted (e.g. software packages).