[zscaler_zia] Add support for new fields in DNS and Web Dataset

[mohitjha-elastic]

Proposed commit message

zscaler_zia: Add support for new fields in DNS and Web Dataset.

This update adds support for newly introduced fields in both the DNS and Web datasets of the 
Zscaler ZIA integration. The field additions are aligned with the latest documentation updates 
and have been referenced from sources [1] and [2] for the Web and DNS datasets respectively. 

[1] https://help.zscaler.com/zia/nss-feed-output-format-web-logs
[2] https://help.zscaler.com/zia/nss-feed-output-format-dns-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 the elastic package locally.
• Start the elastic stack using the elastic package.
• Move to integrations/packages/zscaler_zia directory.
• Run the following command to run tests.

elastic-package test -v

[elasticmachine]

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

[elastic-vault-github-plugin-prod]

🚀 Benchmarks report

To see the full report comment with /test benchmark fullreport

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: b7254c6

cc @mohitjha-elastic

[elasticmachine]

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