Json RPC endpoint does not require content to be base16

[Neylix]

Description

Remove the base16 format for the transaction content.

Created new Json Schema validation method.

Fixes #1232

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

Unit tests

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[bchamagne]

@samuelmanzanera What are you thoughts on this maxItems=255? In the serialization we have no such limitation