Adding an thumbnail ingredient assertion

[aasheptunov]

Adding an thumbnail ingredient assertion.

User story:
As a deveoper , I want to add Thumbnail and Ingredient Thumbnail Assertions , so that implement the logic for adding thumbnails to the manifest so that they are displayed when files are validated in the verifiers.

DoD:

• The Ingredient Thumbnail Assertion class has been added.
• Added logic to extract thumbnail bytes from the Thumbnail Assertion in the previous manifest, followed by writing the extracted bytes to the Ingredient Thumbnail Assertion.
• Ingredient Thumbnail Assertion is integrated into the signing process.
• Logic for retrieving and parsing thumbnails from outside the library has been added.
• Thumbnail Assertion is integrated into the signing process.
• The added logic is covered by unit tests.