Feature:Less strict RecordBuilder

[atimin]

Current problem

I need to initialize the type of a record otherwise I have a null exception during Bucket.writeRecord.

        Record record = Record.builder()
                .entryName("sensor-1")
                .timestamp(timestamp)
                .type("application/octet-stream")
                .body("Record #1".getBytes())
                .build();

Possible solution

The default content type is "application/octet-stream". Additionally let's rename it to content_type as it is called in the other SDKs.

Additional context

No response

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