[zscaler] Mark package as deprecated

[andrewkroh]

What does this PR do?

There are now Zscaler ZIA and Zscaler ZPA integrations that are specific Zscaler products.
This package is being marked as deprecated. The new integrations are not generated parsers
based on rsa2elk.

Relates #2459

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.

Related issues

• Relates [zscaler_zia] Add ZScaler ZIA package. #2459

[elasticmachine]

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

[elasticmachine]

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• Start Time: 2022-02-16T19:49:41.734+0000

• Duration: 27 min 4 sec

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