NIFI-14571: Add VerifiableFlowRegistryClient interface to verify Flow Registry Client implementations

[mattyb149]

Summary

NIFI-14571 This PR adds a VerifiableFlowRegistryClient interface to nifi-api to enable FlowRegistryClient implementations to verify their configurations. Implementation will be done in separate PRs against the nifi repo, to include code to add the Verify button to the configuration dialog that will call this new interface's method(s), and implementations of the interface for the various FlowRegistryClient implementations.

Tracking

Please complete the following tracking steps prior to pull request creation.

Issue Tracking

• Apache NiFi Jira issue created

Pull Request Tracking

• Pull Request title starts with Apache NiFi Jira issue number, such as NIFI-00000
• Pull Request commit message starts with Apache NiFi Jira issue number, as such NIFI-00000

Pull Request Formatting

• Pull Request based on current revision of the main branch
• Pull Request refers to a feature branch with one commit containing changes

[exceptionfactory]

Thanks for moving this effort forward @mattyb149. I noted a couple changes needed for the package name and interface name to align with existing conventions.

[exceptionfactory]

Thanks for making the corrections @mattyb149, this looks good! +1 merging

[exceptionfactory]

Looks like the commit needs to be signed, then this will be ready to go.