Fm/task/unst 9414 cleanup autotimestep

[thomas-pijls]

What was done

• Changed ja_timestep_auto variable name to autotimestep
• Parameterized autotimestep options
• Made a clear distinction between production (1,3,4,5) and research/hidden (0,2,6-10) autotimestep parameters
• Removed developer option for autotimestep
• Cleaned up and added clear comments to autotimestep code

Evidence of the work done

• Clear from the issue description

Tests

• Not applicable

Documentation

• Add description of production parameters to User Manual
• Add description of all parameters to Tech Ref

Issue link