aerodynamic_analysis (schueltke): add initial cruise Mach polar automatically

Description

Adds now automatically the initial cruise Mach number polar to the polar set given in the config file, if not already available. This allows for automated studies in initial_cruise_mach_number

Related Issue(s)

• Fixes #95

Other Changes

• cleaned code for readFlightConditions

Screenshots/Logs

N.A

Testing Instructions

1. Download this branch and compile aerodynamic_analysis
2. Change initial_cruise_mach_number in aircraft exchange file to a one that is not existing in flight conditions from aerodynamic_analysis_conf.xml
3. Have fun. The polar is added an calculated in addition to those in flight conditions

Developer Checklist

• Code has been tested locally and/or in pipeline.
• documentation updated.
• Merge conflicts resolved with the target branch.

Additional Notes

N.A