Plan to replace `embulk-output-bigquery` with trocco-io's `embulk-output-bigquery_java`

`embulk-output-bigquery` has a long history. It started as a File Input plugin written in Java, and then it was totally rewritten as an Input Plugin written in Ruby.

Now, Embulk is going to make JRuby optional through v0.10. Maintaining Ruby plugins is less prioritized.

In addition, we are seeing several problems around `embulk-output-bigquery` -- although it does not look like a problem of the plugin, but a kind of JRuby and JRE.
* https://github.com/embulk/embulk/issues/1214
* https://github.com/embulk/embulk/issues/1148
* https://github.com/embulk/embulk/issues/978

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https://github.com/trocco-io has developed and is maintaining `embulk-output-bigquery_java`, which is a Java-based plugin aimed to be compatible with existing Ruby-based `embulk-output-bigquery`.
* https://github.com/trocco-io/embulk-output-bigquery_java

We've discussed with https://github.com/trocco-io, and we agreed to replace the existing `embulk-output-bigquery` with their `embulk-output-bigquery_java` after it achieves sufficient compatibility.