Replace branches with tags for EarthWorksOrg externals

[gdicker1]

This affects the ccs_configs, cam, cmeps, cime, mpas-ocean, mpas-seaice, and mpas-framework externals and introduces no code or science changes.

[gdicker1]

As of the writing of this comment, here is where HEAD points to for the earthworks branch of each EarthWorksOrg external. This list can be used to verify that the tags don't use different commits.

• ccs_config: 471a9ce
• cam: 6efe3c5
• cmeps: c6a12d3
• cime: 9a3cb7c
• mpas-ocean: 61bca8e
• mpas-seaice: 9232311
• mpas-framework: 946b5f6