Add two internal session variable info: InPacketBytes, OutPacketBytes

[yibin87]

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  Add two internal session variable info docs-cn#21400
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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the documentation by including details for two new internal session variables, InPacketBytes and OutPacketBytes. These additions provide clarity on their purpose as internal metering tools, ensuring that the documentation accurately reflects the system's current state regarding session-level metrics.

Highlights

• Documentation for new internal session variables: Added documentation for two new internal session variables, InPacketBytes and OutPacketBytes, which are used for internal metering and are not visible to users.

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Changelog

• system-variables.md
  • Added documentation for InPacketBytes internal session variable.
  • Added documentation for OutPacketBytes internal session variable.

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[gemini-code-assist]

Code Review

This PR adds documentation for two new internal session variables, InPacketBytes and OutPacketBytes. The documentation is minimal. I've suggested improvements to make it more consistent with the rest of the document by adding properties like Scope and Type, and improving the description.

A note on style: the variable names InPacketBytes and OutPacketBytes use PascalCase, which is inconsistent with the snake_case convention used for all other system variables in this file. While this might be the actual variable names in the code, it's worth noting this inconsistency for future reference.