proofpoint_tap: clarify use of {source,destination}.ip

[efd6]

What does this PR do?

This adds a note to explain the semantics of {source,destination}.ip for the click datasets. The meaning of these fields in this context have caused confusion for some users.

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

• [ ]

How to test this PR locally

Related issues

Screenshots

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2022-08-10T04:25:15.401+0000

• Duration: 18 min 13 sec

Test stats 🧪

Test	Results
Failed	0
Passed	53
Skipped	0
Total	53

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (4/4)	💚
Files	100.0% (4/4)	💚 2.473
Classes	100.0% (4/4)	💚 2.473
Methods	100.0% (62/62)	💚 9.775
Lines	98.188% (1084/1104)	👍 8.405
Conditionals	100.0% (0/0)	💚

[elasticmachine]

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