Actuator Disk Tutorial

[EttoreSaetta]

Proposed Changes

Hello to everyone,
I added a tutorial for the actuator disk with variable load in the Tutorials repository.
Because of this I changed the regression tests moving from parallel_regression.py to tutorials.py.
Hope this could be useful.

Related Work

PR from SU2 repository: #1027
PR from su2code.github.io repository: #44
PR from Tutorials repository: #4

PR Checklist

• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings (try with the '-Wall -Wextra -Wno-unused-parameter -Wno-empty-body' compiler flags, or simply --warnlevel=2 when using meson).
• My contribution is commented and consistent with SU2 style.
• 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.