Prevent Viewport from panning v2

[glauni]

Hi there,

i'd like to limit how far one can pan the camera with sigma.

    Sigma.js version : 2.2.0
    Graphology version : 0.24.1
    Operating system: MacOS (Monterey 12.4)
    Web browser: Firefox 102.0.1 (64-Bit)

Ive used this before, but it doesnt work with sigma v2 anymore.

Looking forward to do this myself if i find the time.

[ping40]

#metoo