helm: add named template that creates the specification for a cronjob

[audrium]

closes #695

To test:

• set the cronjob schedules to run every minute "* * * * *"
• compare the spec (kuebctl describe <cronjob_pod_name> or k get pod <cronjob_pod_name> -o yaml) with the one which was not using the cronjob_spec named template

Note: I found out that resource-quota-update and retention-rules-apply cronjobs were not using reana infrastructure service account and introduced this change

[codecov-commenter]

Codecov Report

Merging #701 (7c454a3) into master (35f42c5) will not change coverage.
The diff coverage is n/a.

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Additional details and impacted files

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  Lines        2144     2144           
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  Hits          404      404           
  Misses       1740     1740