[fix][io] KCA: Option to use kafka connector's SourceConnector class to create task and task config

[dlg99]

Motivation

KCA's SourceConnector uses Kafka's task name as a parameter and creates the task directly.
this works well enough for simpler or old sources (e.g. deebzium's potgre/mysql/mongo etc).
Actual expected life cycle is to create a connector, then get the task class and the task config from it.
Connectors that rely on such cycle do not work with KCA, e.g. yugabyte's debezium source. See
https://apache-pulsar.slack.com/archives/C5Z4T36F7/p1677506713032549 for details.

Modifications

Added option to pass source connector's class name, made use of it.
Kept the KCA compatible with old configuration, falling back to the legacy behavior if the config is not set.

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This change added unit test.

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• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

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