Adding an action assertion

[aasheptunov]

Adding an action assertion.

User story:
As a deveoper , I want to implement the logic for adding Actions Assertion, so that comply with the C2PA v2.4 specification and ensure that actions are logged in the manifest.

DoD:

• The logic for adding Actions Assertions has been implemented.
• Actions Assertion integrates into the signing process with a placeholder action named c2pa.created.
• The relevant tests have been updated.