[FEATURE] convert symbolic assumptions to constraints

[pvogt09]

Is your feature request related to a problem? Please describe.
No.

Describe the solution you'd like
Symbolic constraints of gain coefficients (variables of type sym) should be checked for assumptions and the assumptions should be converted to constraints on the gain coefficients in the resulting problem in dependance of a user-defined option to control this behaviour.
For example,

x = sym('x');
assume(x >= 0);
K_bounds = x <= 5;

should result in K_bounds equal to $0 <= k <= 5$ instead of only $k <= 5$.

Describe alternatives you've considered
None.
Additional context
None.