Feature: Make xtgeo dependency optional

[oysteinequinor]

xtgeo is a rather large and complicated dependency. We are having big issues with building on Mac M-series and issues due to xtgeo pinning certain versions of dependencies.

We are not using any xtgeo functionality in fmu_sumo, and would like to avoid dealing with it.

Would you be open to making the xtgeo dependency optional?

[equinor-ruaj]

Looking into:

• Make xtgeo an optional dependency
• Lazy loading xtgeo
• Warning trying to use xtgeo method, but it is not installed
• Check with xtgeo team: Can they fix the version pinnings that cause trouble?

[oysteinequinor]

We are using a fork with this commit. Might be a starting point if you want to go in that direction.
oysteinequinor@33eca4d