Remove DTR references in preparation for retirement in March

There are two references to DTR in this project:

https://code.vt.edu/it-common-platform/platform-support/apps/dashboard/-/blob/main/docker-compose.yml#L3

https://code.vt.edu/it-common-platform/platform-support/apps/dashboard/-/blob/main/client/src/components/Namespaces/SealedSecrets/RegistryForm.js#L38

The second one simply needs the reference to dtr.it.vt.edu removed. The first one needs either updated to point to an image on code.vt.edu rather than dtr.it.vt.edu/devcom/devcom-localhost-proxy:traefik-2.3 , or the reference to local development removed and the Docker compose file removed.