R1:07fc8f17ccae

Support "ssl.chain" in Aphlict configuration

Summary: Fixes T10806. Although browsers don't seem to care about this, it's more correct to support it, and the new test console uses normal `cURL` and does care.

Test Plan:
- Hit the error case for providing a chain but no key/cert.
- Used `openssl s_client -connect localhost:22280` to connect to local Aphlict servers.
- With SSL but no chain, saw `openssl` fail to verify the remote.
- With SSL and a chain, saw `openssl` verify the identify of the…