Add modified and created properties

[coverbeck]

Description
Add modified and created properties to hits data structure.

Going to use this for tracking whether we should
look for new hits or not.

Review Instructions
Hard to review on its own, test overall as part of SEAB-6668 review.

Issue
SEAB-6668

Security and Privacy

If there are any concerns that require extra attention from the security team, highlight them here.

e.g. Does this change...

• Any user data we collect, or data location?
• Access control, authentication or authorization?
• Encryption features?

Please make sure that you've checked the following before submitting your pull request. Thanks!

• Check that you pass the basic style checks and unit tests by running mvn clean install
• Ensure that the PR targets the correct branch. Check the milestone or fix version of the ticket.
• Follow the existing JPA patterns for queries, using named parameters, to avoid SQL injection
• If you are changing dependencies, check the Snyk status check or the dashboard to ensure you are not introducing new high/critical vulnerabilities
• Assume that inputs to the API can be malicious, and sanitize and/or check for Denial of Service type values, e.g., massive sizes
• Do not serve user-uploaded binary images through the Dockstore API
• Ensure that endpoints that only allow privileged access enforce that with the @RolesAllowed annotation
• Do not create cookies, although this may change in the future
• If this PR is for a user-facing feature, create and link a documentation ticket for this feature (usually in the same milestone as the linked issue). Style points if you create a documentation PR directly and link that instead.