[Cisco_Secure_Endpoint] Add drop processor for empty events

[P1llus]

What does this PR do?

If there are no events for the 24 hour interval, the Cisco API endpoint returns an empty data array, and the ingest pipeline processor returns processor failures because of this.

Its better to drop the empty event rather than storing ingest failures.

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.

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Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[ShourieG]

LGTM

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• Start Time: 2022-11-25T12:26:48.279+0000

• Duration: 15 min 8 sec

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Test	Results
Failed	0
Passed	13
Skipped	0
Total	13

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (1/1)	💚 4.444
Classes	100.0% (1/1)	💚 4.444
Methods	93.75% (15/16)	👍 5.315
Lines	89.216% (455/510)	👎 -3.368
Conditionals	100.0% (0/0)	💚

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Package cisco_secure_endpoint - 2.7.1 containing this change is available at https://epr.elastic.co/search?package=cisco_secure_endpoint