Avoid name clashes when multiple Helm tasks run (in parallel)

[michaelsauter]

A few issues have been observed when multiple Helm tasks run, e.g. because there is more than one chart, or because the same chart should be deployed to multiple places:

• the generated artifacts (such as the diff) should have the e.g. target cluster + source chart in the name
• the packaged helm archive should have e.g. the source chart in the name to avoid race conditions if multiple tasks run in parallel

[michaelsauter]

Transferring as a consequence of opendevstack/ods-pipeline#722.