feat: Depend on the `semantic_release` job when generating a Helm chart.

This MR adds a dependency on the `semantic_release` job, so that by the time
the Helm chart is being generated the Git tag for the release already exists.

The file uses `!reference` tags to ensure that deployments run under the same
circumstances as the `semantic_release` job.

We also want to create a Helm chart during a merge request pipeline, but not
upload it to the registry. Since we cannot conditionally add a `needs:` keyword
for branch pipelines only, this creates two separate jobs that use the
`extends:` keyword to minimize duplication.

Issue: team#335