[Zeek] Add NTP and Signature data streams

[legoguy1000]

What does this PR do?

Adds the NTP and Signature data streams that weren't transfer from elastic/beats#23772 and elastic/beats#24224. Also found that the zeek.connection.id field was being left as an empty object {} so I added a remove for that.

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.
• If I'm introducing a new feature, I have modified the Kibana version constraint in my package's manifest.yml file to point to the latest Elastic stack release (e.g. ^7.13.0).

Author's Checklist

• [ ]

How to test this PR locally

cd integrations/packages/zeek
elastic-package check && elastic-package stack down && elastic-package build && elastic-package stack up -d -v -p default && eval "$(elastic-package stack shellinit)" && elastic-package test  -v --data-streams ntp,signature,connection

Related issues

• closes Zeek Integration missing #1461

Screenshots

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Build stats

• Start Time: 2021-09-09T12:36:47.136+0000

• Duration: 58 min 38 sec

• Commit: 3882f90

Test stats 🧪

Test	Results
Failed	0
Passed	201
Skipped	0
Total	201

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