[Fixes] Update gallery app readme and customAction parameter type

[eriqua]

Description

• Update customAction parameter type to array as expected by the API
• Rerun the readme utility to fix previously failing module static validation

Pipeline references

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Pipeline

Type of Change

Please delete options that are not relevant.

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Update to documentation

Checklist

• I'm sure there are no other open Pull Requests for the same update/change
• My corresponding pipelines / checks run clean and green without any errors or warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (readme)
• I did format my code

[ChrisSidebotham]

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