[feat] Support auto download schema when create producer.

[shibd]

Motivation

If a schema exists in a topic, but the producer does not know it. He still wanted to send data to the topic. (The scenario in which the DLQ sends a message: Please refer #139 [Verifying this change][5])

Modifications

• When creating a producer with autoDownloadSchema param, try to get the schema of that topic and use it.
• Support getSchema on LookupService(HTTP and Binary).

Verifying this change

• Add LookupServiceTest unit test to cover getSchema logic.
• Add SchemaTest.testAutoDownloadSchema unit test to cover creating producer success when the topic has a schema.

Documentation

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[shibd]

Job failure seems to have a flaky test, can help review and rerun the job? @BewareMyPower