Update top level config params

[brynpickering]

Fixes #496 with new parameter names and no equals or scale.

Fixes issue #452

EDIT: is automatically the case Possible TODO: allow init kwargs to be passed to the built-in example models on their initialisation (e.g., calliope.examples.national_scale(override_dict={"config.init.subset_time": ...}) -> calliope.examples.national_scale(subset_time=...))

TODO: add top-level parameter tests.

Summary of changes in this pull request:

• run and model config split into init/build/solve config keys with a flat dict layout in each.
• parameters moved out of config into a top-level parameters key with a syntax discussed in Separate top-level config and parameters  #452 and in a number of discussions.

Reviewer checklist:

• Test(s) added to cover contribution
• Documentation updated
• Changelog updated
• Coverage maintained or improved

[codecov]

Codecov Report

Merging #497 (b9d1e34) into main (c53bfa7) will increase coverage by 0.15%.
The diff coverage is 93.77%.

@@            Coverage Diff             @@
##             main     #497      +/-   ##
==========================================
+ Coverage   92.20%   92.36%   +0.15%     
==========================================
  Files          32       32              
  Lines        4016     4045      +29     
  Branches      957      956       -1     
==========================================
+ Hits         3703     3736      +33     
+ Misses        198      196       -2     
+ Partials      115      113       -2     

Files	Coverage Δ
src/calliope/backend/backend_model.py	97.40% <100.00%> (+2.11%)	⬆️
src/calliope/backend/helper_functions.py	99.37% <100.00%> (+0.01%)	⬆️
src/calliope/backend/pyomo_backend_model.py	95.66% <100.00%> (ø)
src/calliope/backend/where_parser.py	98.52% <100.00%> (-0.04%)	⬇️
src/calliope/core/attrdict.py	99.50% <100.00%> (ø)
src/calliope/core/util/tools.py	91.89% <100.00%> (+0.11%)	⬆️
src/calliope/examples.py	100.00% <100.00%> (ø)
src/calliope/postprocess/results.py	90.32% <100.00%> (ø)
src/calliope/preprocess/model_data.py	99.11% <100.00%> (+0.17%)	⬆️
src/calliope/preprocess/time.py	72.85% <100.00%> (-3.20%)	⬇️
... and 6 more

... and 1 file with indirect coverage changes