Multiline config option values and Paraview vtu default output

[talbring]

Proposed Changes

This PR just contains two small changes:

1. I added the capability to use multi-line statements in the config file. That should make the file a little bit more readable, especially for list options. To continue a statement in the next line, use \ at the end of the current line. Commented lines and everything after the \ are skipped. That means the following way to specify an option works now:

SCREEN_OUTPUT=(INNER_ITER, \ % A comment that is ignored
               WALL_TIME, \
               RMS_DENSITY, \
               LIFT, \
               DRAG, \
              %CAUCHY_SENS_PRESS, \ Option value is ignored
               CAUCHY_DRAG, \
              %RMS_ADJ_DENSITY, \ Option value is ignored
               RMS_ADJ_ENERGY)

Furthermore, if an error occurs now during the processing of the config file, the line number is also printed in order to quickly identify the location.

2. Paraview XML format is now the default format (*.vtu) if the option OUTPUT_FILES is not present. I wanted to do that already when I added the XML format in January, but I simply forgot... The old format can be used with PARAVIEW_LEGACY and SURFACE_PARAVIEW_LEGACY.

Related Work

Resolve any issues (bug fix or feature request), note any related PRs, or mention interactions with the work of others, if any.

PR Checklist

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• I have added a test case that demonstrates my contribution, if necessary.
• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp) , if necessary.

[pcarruscag]

Multiple lines?! Take my money!

[TobiKattmann]

Thanks for this 💐
It makes especially DEFINITION_DV a lot easier to handle:)

[TobiKattmann]

can you add a short description here

[TobiKattmann]

a small comment here maybe like "# Unify lines that end with a continuation char '' "