feat(rust/signed-doc): Add validation rule to check authors of new doc version match previous those in version.

[saibatizoku]

Description

Implements the functional validation of a new doc version that verifies that the authors of the previous (latest) version are exactly the same.

Considerations

Current specifications do not clearly state what the validation of author signatures should involve. For example, does signature order matter? can there be new authors?

Closes #492 .

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my 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 module

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 425/425}$ | ${\color{red}Fail: 0/425}$ |

[Mr-Leshiy]

LGTM