In metadata, reformat params_str

[capelastegui]

column params_str in the forecast metadata table currently has the following format:

[-4.3e+02 -2.4e-04  5.3e+02]

We could make it more useful by adding commas:

[-4.3e+02 -2.4e-04  5.3e+02]

, as this version is something that we can paste on python code to get a real list.

[capelastegui]

We are using built-in numpy array formatting, which doesn't quite work as we want:

a_tmp = np.array([1.00000001,2,0.00000003])
print(a_tmp)
print(np.array_repr(a_tmp, precision=3))
print(np.array_str(a_tmp, precision=3))

output:

[1.00000001e+00 2.00000000e+00 3.00000000e-08]
array([1.e+00, 2.e+00, 3.e-08])
[1.e+00 2.e+00 3.e-08]