Update ARGS for to streamline customer delivery

[cmaynard-ngwpc]

In order to facilitate easier merging of NGWPC code to the parent OWP repositories, several Dockerfile ARG entries have been streamlined and moved to the top.

Additions

• Added ARG IMAGE_NAMESPACE
• Instructions in a comment at the top specifying which ARG's to update when this Dockerfile is adopted by OWP

Changes

• ARG ORG changed to ARG GHCR_ORG
• Use GH_ORG when referencing the nwm-msw-mgr GitHub repository.
• ARG EWTS_ORG changed to ARG GH_ORG and moved to the top of the Dockerfile
• Moved ARG EWTS_REF to the top of the Dockerfile
• ARG MSW_MGR_VERSION changed to ARG MSW_MGR_REF and moved to the top of the Dockerfile
• Use IMAGE_NAMESPACE in place of ngwpc in the Dockerfile LABEL declaration

[miguelp1986]

Pipeline passes with changes. Approved.