okta: mark api_key config field as required

[efd6]

What does this PR do?

This fixes the configuration requirements for the okta api_key.

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.

Author's Checklist

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How to test this PR locally

Related issues

• Fixes [okta] API Key should be labelled as required. #4105

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• Start Time: 2022-09-12T08:51:31.673+0000

• Duration: 21 min 56 sec

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Test	Results
Failed	0
Passed	12
Skipped	0
Total	12

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Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (1/1)	💚
Classes	100.0% (1/1)	💚
Methods	100.0% (17/17)	💚
Lines	86.69% (495/571)	❕
Conditionals	100.0% (0/0)	💚

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[andrewkroh]

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