Add configuration for service loader

[martinholt]

Problem

When Connect is started using the plugin discover mode "service_load" the Jdbc Sink and Source connectors are not found during classpath scanning

Solution

Add configuration for Service Loader to discover the connectors

Does this solution apply anywhere else?

• yes
• [ x] no

If yes, where?

Test Strategy

Tested locally on Connect using this fork

Testing done:

• Unit tests
• Integration tests
• [x ] System tests
• [ x] Manual tests

Release Plan

Merge to master

[confluent-cla-assistant]

🎉 All Contributor License Agreements have been signed. Ready to merge.
✅ martinholt
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