Provide solver-agnostic way to set warm_start/MPC friendly setting

After https://github.com/ami-iit/qpsolvers-eigen/pull/15 , if a user is using a solver in a warm start setting, it needs to call the following code:

~~~cxx
// Set osqp-specific parameters
if (solver.getSolverName() == "osqp")
{
// solver.setBooleanParameter("verbose", false);
solver.setBooleanParameter("warm_starting", true);
}

// Set proxqp-specific parameters
if (solver.getSolverName() == "proxqp")
{
solver.setStringParameter("initial_guess", "WARM_START_WITH_PREVIOUS_RESULT");
}
~~~

This is objectively a bit ugly, perhaps we could support plugin-defined setting presets, so we could have something like:

~~~
solver.setSettingsPreset("warm_start")
~~~

that under the hood sets the correct parameter in the solver, leaving all the other parameters set to their current values. Having such a flexible method, then the semantics of a given settings preset can be either defined at the `qpsolvers-eigen` level, or even just for a subset of the solvers plugin.

fyi @LoreMoretti @GiulioRomualdi

I think it could be worth to understand how to integrate this and https://github.com/ami-iit/qpsolvers-eigen/issues/8 .