BATCH-2847: Add getUniqueJobParametersBuilder() in JobLauncherTestUtils

[jojoldu]

JobLauncherTestUtils often uses the getUniqueJobParameters method.
But it seems a bit cumbersome to use this method with other JobParameters.
In the same case, I use it like this:

new JobParametersBuilder(jobLauncherTestUtils.getUniqueJobParameters())
.addString()
.addDouble()

I want to make this convenient.

jobLauncherTestUtils.getUniqueJobParametersBuilder()
.addString()
.addDouble()

[fmbenhassine]

LGTM. Rebased, squashed and merged as 60bbc00.

@jojoldu Thank you for your contribution!

[jojoldu]

@benas Oh, Thanks.

I hope I can contribute next time.
Thanks again.