Simplify and update Docker build mechanism

Currently, in our Dockerfile we recompile OTB from source. This should not be necessary, there are other possibilities:

• Make our Python image dependant of OTB pre buit images.
• With OTB 9, just download precompile binaries and recompile Python bindings.

Additionnaly, we should update the Ubuntu image used at least to 22. A change could be made upstream in OTB docker images.