CloudRun - Support listing jobs with a label

**Describe the solution you'd like**

We would like to be able to list CloudRun job using a filter.
Something like the following code snippet (which didn't work yet as there is no `setFilter()` method).

```java
var jobsClient = JobsClient.create();
var existingJob = jobsClient.listJobs(ListJobsRequest.newBuilder()
.setParent(String.format("projects/%s/locations/%s", projectId, region))
.setFilter("labels.key=value")
.build();
```

**Describe alternatives you've considered**
The alternative is to list all jobs and filter later.
However, this didn't scale if there were a lot of jobs.

**Additional context**
It is already possible via gcloud: `gcloud run jobs list --filter "labels.key=value"`.

Start with the Java JobsClient.listJobs entry point and its ListJobsRequest builder, comparing the requested label-filter behavior with the gcloud run jobs list --filter command. Done means callers can list Cloud Run jobs using a label filter instead of fetching every job first, with the relevant client behavior covered by tests.

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