Add Java code sample for table inspection

[jakubrauch]

To be linked from https://cloud.google.com/dlp/docs/inspecting-structured-text

Fixes #issue

It's a good idea to open an issue first for discussion.

• [yes, except where consistency made more sense] I have followed Sample Format Guide
• [yes] pom.xml parent set to latest shared-configuration
• [nothing new] Appropriate changes to README are included in PR
• [nothing new] API's need to be enabled to test (tell us)
• [nothing new] Environment Variables need to be set (ask us to set them)
• [yes] Tests pass (mvn -P lint clean verify)
  • (Note- Checkstyle passing is required; Spotbugs, ErrorProne, PMD, etc. ERROR's are advisory only)
• [yes] Please merge this PR for me once it is approved.

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