featuregate analyzer: use 1 week lookback if possible

[stbenjam]

Allow a 1-week lookback if it's sufficient, to avoid a long tail of a regression into the historical results

[openshift-ci]

Hello @stbenjam! Some important instructions when contributing to openshift/api:
API design plays an important part in the user experience of OpenShift and as such API PRs are subject to a high level of scrutiny to ensure they follow our best practices. If you haven't already done so, please review the OpenShift API Conventions and ensure that your proposed changes are compliant. Following these conventions will help expedite the api review process for your PR.

[deads2k]

/lgtm
/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: deads2k, stbenjam

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[openshift-bot]

[ART PR BUILD NOTIFIER]

Distgit: ose-cluster-config-api
This PR has been included in build ose-cluster-config-api-container-v4.18.0-202408222209.p0.g717c5f8.assembly.stream.el9.
All builds following this will include this PR.