[SANTUARIO-615] Implementation pre-post processing extension with xades (basic) example.

[jrihtarsic]

The purpose of this PR is to present the proposals [SANTUARIO-615] for the pre/post processor for the signatures.
The use case is the request for XAdES support as requested in SANTUARIO-402 and SANTUARIO-416. The use-case already supports (Basic Signatures profile) and (with the right certificate) it pass the validation by EC DSS tool:
https://ec.europa.eu/digital-building-blocks/DSS/webapp-demo/validation

Please note that for "composing" the "XAdES" data, the generated jaxb objects are used from the xades scheme v1.4.1 and v1.3.2.

This is a experimental PR to discuss/verify the following architectural approaches for the XAdES:

• the pre-post processing design pattern for signing (Is the approach accepted, in example is used one interface, or it wold be better to have each own for pre and post processing,.. )
• use of jaxb generated objects with jakarta.xml.bind.(Marshaller|Unmarshaller).Currently xmlsec is using internal jaxb implementation using ElementProxy for some parts and for others DOMStructure/XMLStructure both with with internal/own/(non generated) "jaxb" object.