feat(dart/catalyst_cardano_serialization): x509 self-signed certificate

[dtscalac]

Description

• Adds X509 self signed certificate generator
• Updates example app to submit the self-signed cert with RBAC transaction

Related Issue(s)

Closes #791

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 | ${\color{lightgreen}Pass: 211/211}$ | ${\color{red}Fail: 0/211}$ |

[damian-molinski]

lgtm