Added contact sales includes to CODEOWNERS

Why is this change being made?

I made a change to /source/includes/contact-sales.html.haml and @dmor pointed out that file isn't included in CODEOWNERS.

@brandon_lyon @skarpeles do y'all have any suggestions for other includes we need to add to CODEOWNERS?

cc @sbouchard1 added you as an owner, we can add other folks there too

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
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