docs(iam): update comments and terminology in IAM samples

[eapl-gemugami]

Description

Follow-up of #13010 and #13097

Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• Tests pass: nox -s py-3.13 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• Please merge this PR for me once it is approved

[code-review-assist]

Hi team,

I'm currently reviewing this pull request and will provide my feedback shortly. In the meantime, here's a summary of the changes for you and other reviewers to quickly get up to speed:

This pull request, submitted by @eapl-gemugami, updates comments and terminology in IAM samples. The goal is to improve clarity and consistency across the documentation. Specifically, the changes involve replacing the term "member" with "principal" in several files to reflect best practices and Google Cloud's terminology.

Here's a breakdown of the changes:

• Files Modified:

  • iam/cloud-client/snippets/iam_modify_policy_add_role.py: Changed parameter member to principal in modify_policy_add_role function (lines 17-23).
  • iam/cloud-client/snippets/modify_policy_add_member.py: Changed parameter member to principal, updated docstring to reference principal IDs, and removed outdated member format examples (lines 24-41 and 50-55).
  • iam/cloud-client/snippets/modify_policy_remove_member.py: Changed parameter member to principal, updated docstring to reference principal IDs, and removed outdated member format examples (lines 24-41).
  • iam/cloud-client/snippets/quickstart.py: Changed parameter member to principal throughout the quickstart function and updated comments to reflect the change (lines 21-51, 79-98, 102-127).

• Summary of Changes: The core change is a consistent renaming of the member parameter to principal across multiple IAM sample files. The documentation has also been updated to improve clarity and point to the correct documentation for principal ID formats.

The author has indicated that all tests and lint checks have passed.

Let me know if you have any questions.

And now, a little haiku to brighten your day:

Code flows like a stream,
Clear and concise, a clean fix,
Review's swift and kind.

[code-review-assist]

This pull request updates comments and terminology in IAM samples, replacing "member" with "principal." This change improves clarity and aligns the samples with current IAM documentation. The changes are well-implemented and follow the sample guidelines. I have referenced the Sample Guidelines from AUTHORING_GUIDE.MD, specifically the sections on Coding Style, Documenting Arguments, and Documenting Types, in this review.