Assorted deployment fixes

While cleaning up the way we deploy the indexer journal clients, a handful of inconsistencies have been noticed:

• the config uses the journal key instead of the more common journal_client
• the cli explodes when redundant arguments are set (e.g. cls=kafka)
• the cli overrides the object types (which is fine, but print a warning to avoid surprises)

assigned to @olasd

mentioned in issue swh/infra/sysadm-environment#5200 (closed)

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merged