introduce 'ci_cron_schedule' for scheduled CI actions

[chdoc]

This enables scheduled runs for actions-based CI via a new variable called ci_cron_schedule. As discussed in #77, there is no default value to keep everyone from using the same value.

closes: #77

[erikmd]

LGTM, thanks @chdoc.

Three small suggestions/questions:

• could you mention the implied timezone? (according to https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#onschedule, it's UTC)
• are you sure that when writing '{{ ci_cron_schedule }}' in the mustache file, it won't add an extra quoting? (didn't test right now)
• would it be worth it, to add in the description, a remark like this? "Also, projects may prefer different intervals, such as daily or weekly builds."

[chdoc]

could you mention the implied timezone? (according to https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#onschedule, it's UTC)

done!

are you sure that when writing '{{ ci_cron_schedule }}' in the mustache file, it won't add an extra quoting? (didn't test right now)

If I add ci_cron_schedule: '5 4 * * *' to my meta.yml, the diff I get is:

on:
+  schedule:
+    - cron: '5 4 * * *'
   push:

So I think the quoting is as it should be.

would it be worth it, to add in the description, a remark like this? "Also, projects may prefer different intervals, such as daily or weekly builds."

I commented the examples to explain that one of them is weekly while the other is daily.

[Zimmi48]

Thanks!