[DLP] Implemented dlp_inspect_image_all_infotypes with unit test cases

[Avani-Thakker-Crest]

Description

[DLP] Implemented dlp_inspect_image_all_infotypes with unit test cases. Java equivalent: https://cloud.google.com/dlp/docs/inspecting-images.md#dlp-inspect-image-all-infotypes-java

Fixes #

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Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.9 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• Please merge this PR for me once it is approved.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample

[snippet-bot]

Here is the summary of changes.

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• dlp/snippets/inspect_content.py:933, tag dlp_inspect_image_all_infotypes

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