Setting group options from configuration file

[christophe-david]

This PR allows setting values of options for an OpenMDAO group.

In particular, it will allow using the auto_order feature introduced by OpenMDAO 3.28.

As for FAST-OAD modules, options can be set simply by a <key>: <value> in the corresponding section.

This is a bit inconsistent with the settings of linear_solverand nonlinear_solver, that are attributes and not options, and will yet be at the same level in the configuration file. But it looked like it was worth privileging the consistency with the setting of module options.

Documentation has been updated and can be previewed here.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (15b04af) 84.16% compared to head (c2d603b) 84.14%. Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #502 +/- ## ========================================== - Coverage 84.16% 84.14% -0.02% ========================================== Files 132 132 Lines 6061 6068 +7 Branches 891 893 +2 ========================================== + Hits 5101 5106 +5 - Misses 804 806 +2 Partials 156 156 ```

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