imperva_waf: improve config robustness and error reporting

[efd6]

Proposed commit message

imperva_waf: improve config robustness and error reporting

* prevent missing trailing slash from causing collection failure
* avoid misleading errors resulting from collection failure

Note

The CEL input is not tested in system testing. So extra caution is required in review.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.
• I have verified that any added dashboard complies with Kibana's Dashboard good practices

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• [ ]

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cc @efd6

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20.0% Coverage on New Code
0.0% Duplication on New Code

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Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)

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Package imperva_cloud_waf - 1.7.0 containing this change is available at https://epr.elastic.co/package/imperva_cloud_waf/1.7.0/

[mabuzenah]

im using version 1.9.0 and this part of the code is still causing an issue state.url.trim_right("/") + v.worklist[v.next].filename

{"log.level":"error","@timestamp":"2025-03-07T00:47:29.705Z","message":"single event object returned by evaluation","component":{"binary":"filebeat","dataset":"elastic_agent.filebeat","id":"cel-default","type":"cel"},"log":{"source":"cel-default"},"ecs.version":"1.6.0","input_source":"https://logs1.incapsula.com/23630_828048/","input_url":"https://logs1.incapsula.com/23630_828048/","event":{"error":{"code":"401","id":"401 Unauthorized","message":"GET https://logs1.incapsula.com/23630_82804823630_1076173.log: \r\n<title>401 Authorization Required</title>\r\n\r\n

401 Authorization Required

\r\n

---

nginx/1.25.0\r\n\r\n\r\n"}},"log.origin":{"file.line":383,"file.name":"cel/input.go","function":"github.com/elastic/beats/v7/x-pack/filebeat/input/cel.input.run.func1"},"service.name":"filebeat","id":"cel-imperva_cloud_waf.event-1ee7cae5-3f31-4f51-b04c-f542d4020a2e","log.logger":"input.cel","ecs.version":"1.6.0"}