8. Find all integer values of the parameter \(a\) for which the system has at least one solution

\[
\left\{\begin{array}{l}
y-2=x(x+2) \\
x^{2}+a^{2}+2 x=y(2 a-y)
\end{array}\right.
\]

In the answer, specify the sum of the found values of the parameter \(a\).