Add warnings about GitHub API limitations for PRs

[raskinmaya]

Description

There are discrepancies between the schemas of pull requests retrieved from ingestion versus live-events. As a result, some properties can only be calculated when using live-events and are not available during ingestion. Since this limitation originates from the GitHub API itself, we should add a clear warning in the documentation to make users aware of this constraint.

Added docs pages

Updated docs pages

Working Agreements and Measuring PR standards (docs/guides/all/working_agreements_and_measuring_pr_standards.md)

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