Adaptive mesh refinement

Enable adaptive mesh refinements

Info:
- PETSc example 11: [ex11.c](https://petsc.org/main/src/ts/tutorials/ex11.c.html)
- [DMAdaptLabel](https://petsc.org/main/docs/manualpages/DM/DMAdaptLabel/)

Tasks:
- [ ] Add adaptivity capability for steady-state problems
    - use case: mesh convergence study
- [ ] Add adaptivity to transient problems
    - implicit
    - explicit