Add ACCESS-ESM1.6 SBD

[dougiesquire]

I would like to add an initial SBD for ACCESS-ESM1.6. For now, the only difference from the ACCESS-ESM1.5 SBD will be the MOM5 spec.

In ACCESS-ESM1.6, I would like to build MOM5 in the same way as ACCESS-ESM1.5, except using the "master" branch and the "ACCESS-ESM" "type" variant. To allow this, the following changes are required:

In MOM5 SPD:

• Add an "access-esm1.6" version that uses the "master" branch
• Remove the conditional logic from the definition of the "type" variant
• Extend withs and ifs currently set up for @access-esm1.5 to include @access-esm1.6

In ACCESS-ESM1.5 SPD:

• Specify +type=ACCESS-CM in MOM5 spec

In (new) ACCESS-ESM1.6 SPD:

• Specify +type=ACCESS-ESM in MOM5 spec

I'll follow up with a PR shortly.

[CodeGat]

References ACCESS-NRI/ACCESS-ESM1.6#1