OBSINTA-777: [Incidents] Add filtering regression tests

[DavidRajnoha]

Add regression test suite for incidents filtering functionality:

• Individual and combined severity filters (Critical, Warning, Informative)
• State filter combinations (Resolved, Firing)
• Chart interaction behavior with active filters
• Filter persistence after incident selection/deselection

Uses comprehensive filtering scenarios fixture with 12 incidents.

Verifies: OU-727

[openshift-ci-robot]

@DavidRajnoha: This pull request references OBSINTA-777 which is a valid jira issue.

Warning: The referenced jira issue has an invalid target version for the target branch this PR targets: expected the task to target the "4.21.0" version, but no target version was set.

In response to this:

Add regression test suite for incidents filtering functionality:

• Individual and combined severity filters (Critical, Warning, Informative)
• State filter combinations (Resolved, Firing)
• Chart interaction behavior with active filters
• Filter persistence after incident selection/deselection

Uses comprehensive filtering scenarios fixture with 12 incidents.

Verifies: OU-727

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[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: DavidRajnoha
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[openshift-ci]

@DavidRajnoha: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/okd-scos-e2e-aws-ovn	d1f0d4c	link	false	/test okd-scos-e2e-aws-ovn
ci/prow/e2e-aws-ovn	d1f0d4c	link	true	/test e2e-aws-ovn

Full PR test history. Your PR dashboard.

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