Unify Flow and FEA unsteady options + fix unsteady FEA adjoints + add FEA python wrapper examples

[pcarruscag]

Proposed Changes

Use TIME_STEP and MAX_TIME in the FEA solver instead of DYN_*

PR Checklist

• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).
• My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).
• 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.

[kursatyurt]

Nice clean-up/unification