Run the "Cleanup Disk" step in the publish-service-artifacts CI job

[ulucinar]

Description of your changes

Relevant PR: https://github.com/upbound/uptest/pull/192

The failing run for the publish-service-artifacts CI job here reveals that we may be able to benefit from disk cleaning for this job:

This PR adds the Cleanup Disk step for the child jobs of the publish-service-artifact job, which are responsible for building the family packages and pushing them to the registry,

I have:

• [x] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

A test run of the job is here:

Please note the newly introduced Cleanup Disk step for the child builder jobs.

Another successful run is here: https://github.com/upbound/provider-aws/actions/runs/8251670678

[ulucinar]

We had success in building and publishing all AWS family packages in ~53 min with 6 child build jobs here. Please note that this build is from the HEAD of the main branch, where the Terraform CLI and the Terraform provider binaries have been removed from the packages. A release from the 0.x branches can prove to be more problemmatic.

We've used 6 parallel child jobs (30 packages per child job) with a concurrency of 1 for each job for this run as follows: