[zscaler_zia] Add SaaS Security data stream

[brijesh-elastic]

Proposed commit message

zscaler_zia: Add support for SaaS Security data stream.

This data stream collects SaaS Security logs[1] (including Collaboration, CRM, Email,
File, Gen AI, ITSM, Public Cloud Storage, and Repository) using Zscaler ZIA
Nanolog Streaming Service (NSS).

Test samples were derived from documentation and live data samples, 
which were subsequently sanitized.

[1] https://help.zscaler.com/zia/nss-feed-output-format-saas-security-logs

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

How to test this PR locally

• Clone integrations repo.
• Install elastic package locally.
• Start elastic stack using elastic-package.
• Move to integrations/packages/zscaler_zia directory.
• Run the following command to run tests.

elastic-package test -v

[github-actions]

Vale Linting Results

Summary: 10 warnings, 7 suggestions found

⚠️ Warnings (10)

File	Line	Rule	Message
packages/zscaler_zia/_dev/build/docs/README.md	177	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'for example' instead of 'e.g'.
packages/zscaler_zia/docs/README.md	177	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'for example' instead of 'e.g'.
packages/zscaler_zia/docs/README.md	1492	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'and so on' instead of 'etc'.
packages/zscaler_zia/docs/README.md	1492	Elastic.DirectionalLanguage	Don't use directional language. Use 'earlier on this page' instead of 'noted above'.
packages/zscaler_zia/docs/README.md	1493	Elastic.DirectionalLanguage	Don't use directional language. Use 'earlier on this page' instead of 'noted above'.
packages/zscaler_zia/docs/README.md	1494	Elastic.QuotesPunctuation	Place punctuation inside closing quotation marks.
packages/zscaler_zia/docs/README.md	1495	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'for example' instead of 'e.g'.
packages/zscaler_zia/docs/README.md	1496	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'for example' instead of 'e.g'.
packages/zscaler_zia/docs/README.md	1578	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'that is' instead of 'i.e'.
packages/zscaler_zia/docs/README.md	1580	Elastic.Latinisms	Latin terms and abbreviations are a common source of confusion. Use 'that is' instead of 'i.e'.

💡 Suggestions (7)

File	Line	Rule	Message
packages/zscaler_zia/_dev/build/docs/README.md	175	Elastic.Semicolons	Use semicolons judiciously.
packages/zscaler_zia/_dev/build/docs/README.md	179	Elastic.Ellipses	In general, don't use an ellipsis.
packages/zscaler_zia/_dev/build/docs/README.md	181	Elastic.WordChoice	Consider using 'can, might' instead of 'may', unless the term is in the UI.
packages/zscaler_zia/docs/README.md	175	Elastic.Semicolons	Use semicolons judiciously.
packages/zscaler_zia/docs/README.md	179	Elastic.Ellipses	In general, don't use an ellipsis.
packages/zscaler_zia/docs/README.md	181	Elastic.WordChoice	Consider using 'can, might' instead of 'may', unless the term is in the UI.
packages/zscaler_zia/docs/README.md	1533	Elastic.WordChoice	Consider using 'select, press, visits' instead of 'hit', unless the term is in the UI.

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To use Vale locally or report issues, refer to Elastic style guide for Vale.

[elastic-vault-github-plugin-prod]

🚀 Benchmarks report

To see the full report comment with /test benchmark fullreport

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 9fcb49f

cc @brijesh-elastic