[IMP] internal_transfer_with_agreed_amount: clean and standardize code T#71892

[CLaurelB]

Changelog:

• Apply the automatic changes from pre-commit-vauxoo
• Modify license in manifest
• Add or modify the header of xml files having the encoding as UTF-8
• Every xml file must have have one model, the name of that model and the kind of the data, e.g. _data or _demo.
• Modify data putting ids or names in the first position and then their values
• Make improvements in the code for performance or readibility purposes
• Modify setUp to setUpClass improving performance for tests
• Modify inherited record to have the same external id as the original record.
• After refactoring of code, update terms in translation or assigning to the new external ids and move the translation file to i18n folder.

[CLaurelB]

@luisg123v could you review, please?

[CLaurelB]

@luisg123v could you review again, please?

[CLaurelB]

@luisg123v could you review again, please?