add auto value annotation processor to the gradle build

[ttozser]

Without the annotation processor the build fails with an error like this:
BigQueryResult.java:27: error: package AutoValue_BigQueryResult does not exist

See https://github.com/google/auto/blob/master/value/userguide/index.md

[ttozser]

I don't know how this change break the build this way:

bash <(curl -s https://codecov.io/bash) -f BigQueryWorkloadTester/$JACOCO_REPORT_PATH -F BigQueryWorkloadTester
/dev/fd/63: line 1: html: No such file or directory
/dev/fd/63: line 2: syntax error near unexpected token `<'
'
The command "bash <(curl -s https://codecov.io/bash) -f BigQueryWorkloadTester/$JACOCO_REPORT_PATH -F BigQueryWorkloadTester" exited with 2.

[ttozser]

By the way, I don't know if this is intentional or not but the project default branch is dev so the users following the readme land in the dev branch instead of master.

[ldanielmadariaga]

This should be fixed by #243