review defaultBuildDiscarder values

[heurtematte]

The current defaultBuildDiscarder values are defined here:
templates/jenkins/configuration.yml.hbs

- defaultBuildDiscarder:
    discarder:
      logRotator:
        artifactNumToKeepStr: "5"
        numToKeepStr: "128"

I believe the current value for numToKeepStr: 128 is too high and may negatively affect some Jiro instances.

For instance, the EclipseLink instance appears to be impacted by the large number of retained builds.

I propose reviewing the default configuration and replacing it with something more sustainable, such as:

- defaultBuildDiscarder:
    discarder:
      logRotator:
        artifactDaysToKeepStr: "30"
        artifactNumToKeepStr: "5"
        daysToKeepStr: "60"
        numToKeepStr: "10"

This would help reduce build history and retained artifacts by default, which should improve disk usage and overall instance health.

It would also be important to ensure that these default values remain overridable for specific instances when a higher retention policy is needed.