Features used in the shallow convection and the PBL schemes

[oelbert]

Description
This PR adds some namelist parameters for the shallow convection and pbl schemes, as well as some quality of life features for development, namely a "k_select" stencil that is the equivalent of selecting a 2d slice of a 3d field where hte k-index differs for each i and j value, as well as adding the "index_variable" flag for translate tests, for when your test data includes a k-index as a test variable.

How Has This Been Tested?
The shallow convection and pbl scheme translate tests are all run using this branch now

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included

[FlorianDeconinck]

LGTM