install sagemath_giac optional spkg?

from sage-devel, by G. Guninski:

the following fails on 10.6 and https://sagecell.sagemath.org/
```
print(giac.version())
K.<X,Y>=QQ[];I=Ideal([X+Y,X*Y])
I2=I.elimination_ideal(X,algorithm="giac");I2 #fails with exception

"giac 1.9.0, (c)
ModuleNotFoundError: No module named 'sagemath_giac'
```