Add support for aliases like composer-2 in Composer image version field

[modular-magician]

This covers the new aliases for Composer major version (composer-1, composer-2), improved DiffSuppressFunc implementation for image version field, and updates to the related documentation.

Fixes #11217

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Release Note Template for Downstream PRs (will be copied)

composer: Added support for `composer-1` and `composer-2` aliases in image version argument

Derived from GoogleCloudPlatform/magic-modules#5787

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