Rearrange UM_v7 branches to allow further ACCESS-ESM1.5 and ACCESS-ESM1.6 development?

I propose that we create an access-esm1.5 branch of the UM_v7 repository, so that the um7 Spack package can use version access-esm1.5 and branch access-esm1.5 as per the other access-esm1.5 related packages.

This is partly because there is already an ESM1.6 branch, (which should eventually be renamed access-esm1.6 for the sake of consistency).

The ACCESS-ESM1.6 development of UM_v7 should then be able to merge to the main branch until access-esm1.6 is ready to release.

What are your thoughts?