[Iceberg]Refactor validation for SHOW CREATE TABLE for relevant tests

[hantangwangd]

Description

This PR refactor the validation logic for SHOW CREATE TABLE in Iceberg relevant tests.

This refactoring can make these relevant test cases less likely to be affected on adding or modifying table properties. Besides, it can make newly added test cases which have to validate the result of SHOW CREATE TABLE more concise.

Motivation and Context

Make existing test cases less likely to be affected on adding or modifying table properties. See the discussion here

Impact

N/A

Test Plan

This is a test refactoring.

Contributor checklist

• Please make sure your submission complies with our contributing guide, in particular code style and commit standards.
• PR description addresses the issue accurately and concisely. If the change is non-trivial, a GitHub Issue is referenced.
• Documented new properties (with its default value), SQL syntax, functions, or other functionality.
• If release notes are required, they follow the release notes guidelines.
• Adequate tests were added if applicable.
• CI passed.

Release Notes

== NO RELEASE NOTE ==

[steveburnett]

LGTM! (docs)

Pull branch, local docs build, looks good. Thanks!