feat: connection for schema registry

[tabVersion]

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What's changed and what's your intention?

confluent schema registry doc: https://docs.confluent.io/platform/current/schema-registry/develop/api.html

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support connection for schema registry

create connection sr_conn with (
  type = 'schema_registry',
  schema.registry = 'http://...',
  schema.registry.username = '...',
  schema.registry.password = '...'
)