Provide access to the metadata from the python API

Summary

Provides a wrapping of the ImageMetadata object through the Python API, using SWIG.

Rationale

Fix #2226 (closed)

Implementation Details

Classes and files

• Creation of an ImageMetadata.i file to describe the new API.

Applications

• Add a getter/setter to access metadata from the application object

Documentation

• Update the Cookbook with this new API.

Additional notes

This is a work in progress. Before merging, we still need to:

• Wrap the geom metadata
• Wrap the new time metadata (see !868 (merged))
• Modify the Import/ExportImage of the current API so it provides the ImageMetadata
• Update the documentation
• Set up some tests

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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Check before merging:

• All discussions are resolved
• At least 2 👍 votes from core developers, no 👎 vote.
• The feature branch is (reasonably) up-to-date with the base branch
• Dashboard is green
• Copyright owner has signed the ORFEO ToolBox Contributor License Agreement
• Optionally, run git diff develop... -U0 --no-color | clang-format-diff.py -p1 -i on latest changes and commit