ci: run S3 cache purge on dedicated cron

[v-scharf]

Clean all S3 CI cache in one place.

All repos share one CI S3, so purge it centrally instead of per-repo.
A dedicated purge-cache cron cleans all 3 buckets:

• cache → older than 1 day
• dev → older than 14 days
• public → older than 14 days

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

🟢 Coverage ∅ diff coverage · +0.01% coverage variation

Metric	Results
Coverage variation	✅ +0.01% coverage variation (-1.00%)
Diff coverage	✅ ∅ diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (369d386)	91179	22837	25.05%
Head commit (d892323)	91179 (+0)	22847 (+10)	25.06% (+0.01%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3691)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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TIP This summary will be updated as you push new changes.}

[micbar]

We need to give the nightly cron trigger a name, that it doesn't trigger on the purge-cache cron run.