Add TERRL external recipient estimator

[Nickul-MSFT]

Summary

• add a Transport script that estimates TERRL external-recipient usage from Get-MessageTraceV2 data
• add offline classification and pagination tests
• add the documentation landing page and Transport navigation entry

Notes

The estimate is intentionally identified as approximate; Get-LimitsEnforcementStatus remains the live enforcement source of truth.

[azure-pipelines]

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[Copilot]

Pull request overview

Adds a new Transport utility to estimate tenant TERRL external-recipient usage based on Get-MessageTraceV2, along with supporting Pester tests and MkDocs documentation so the script is discoverable and documented.

Changes:

• Introduces Get-TerrlExternalRecipientEstimate.ps1, including classification logic and a Get-MessageTraceV2 continuation-based fetcher with request pacing.
• Adds Pester coverage for offline classification rules and pagination/continuation behavior.
• Adds a new docs landing page and links it into the MkDocs Transport navigation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
Transport/Tests/Get-TerrlExternalRecipientEstimate.Tests.ps1	Adds unit tests for classification and trace pagination/continuation behavior.
Transport/Get-TerrlExternalRecipientEstimate.ps1	New script implementing TERRL estimate logic, trace retrieval, aggregation, and reporting.
mkdocs.yml	Adds the new Transport doc page to the site navigation.
docs/Transport/Get-TerrlExternalRecipientEstimate.md	Documents usage, limitations, parameters, and examples for the new script.