Create a "Code of Conduct" document and handle violation reports

# 🚀 Feature Proposal #

We should consider creating a cisagov-wide "Code of Conduct" document and handling violation reports.

## Motivation ##

When I looked [at the cisagov/cool-system repository's Community page](https://github.com/cisagov/cool-system/community), for example, I noticed that there are two unenabled items there. One is a Code of Conduct document and the other is "Repository admins accept content reports".

## Pitch ##

Aside from an OCD-driven desire for completeness, checking off these other items will make cisagov a more mature GitHub organization.

Review the existing default community health files in the cisagov/.github repository and compare the GitHub Community page with the two missing items described in the issue. Define the required Code of Conduct document and violation-report handling, then verify that both Community page items are enabled.

Written by the indexing model from the issue text.