Add offline support for ESA metakernels

If the user need a ESA metakernel offline or if ESA servers are not available, the tool will now display a warning error and try to use the metakernels available in the cache:

[ESA API] Impossible to fetch `latest` version online. Use local cache instead.
[ESA API] Impossible to fetch `juice_crema_5_0.tm` metakernel at `v400_20221021_001` version online. Use local cache instead.

This will fix #71 (closed).

Other

• Improve the documentation on TourConfig about mk and kernels arguments.
• Fix metakernel PATH_VALUES issue in the test for long kernel directory (> 80 characters)