Add 'timestamp' to /status_reports/ routes

[DimStar77]

The current staging workflow is to add all delete requests to Letter Stagings, irrespective of the fact if the del req is for a Ring or Non-Ring package.

We would like to improve that and allow non-ring del-requests to be staged in adi (no difference made between SR and DelReq). Technicaly, OBS already supports this and the staging workflow is in order.

But we have a small issue: if a delreq is added to adi, the repo gets its ID (which will never change, as no build/rebuilds happen in this adi - a delreq is 'just' a package container, build disabled)

We then have installcheck passing over the staging list and leaving a comment. In case of 'issues' detected, this is properly reported. Those issues can change due to different adi stagings being accepted (e.g. build deps of other packages having changes) - but as we never get a new repo-id, installcheck never looks at the adi again. We would like to 'timebomb' the result of installcheck (e.g 7 days) - but for this to work, OBS should give us the information through the api - as to when the installcheck 'test' stored (the webui shows the information)

e.g on webui, we see:

Checks | installcheck (success - about 8 hours ago)

osc api misses the info about the time:

> osc api /status_reports/built/openSUSE:Factory:Staging:adi:1/standard/x86_64/reports/4b736a58cc61bbf6979c427fcfc23afd
<status_report uuid="4b736a58cc61bbf6979c427fcfc23afd">
  <check name="installcheck" required="true">
    <state>success</state>
    <short_description/>
    <url>https://botmaster.suse.de/go/tab/build/detail/AdiChecker.Factory/3779/Run/1/Run#tab-console</url>
  </check>
</status_report>