Tour java improvements

[gvdongen]

• Incorporated Till's feedback (also fixing pre-release workflow)
• Cleaned up code Java snippets (mainly the calls)
• Improved the JavaTour text
• Added state introspection via psql instead of printing

[cloudflare-workers-and-pages]

Deploying with    Cloudflare Pages

Latest commit:	de5c8e4
Status:	🚫  Build failed.

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[pcholakov]

Some minor suggestions but overall looking great! 👏

[pcholakov]

I recently discovered the curl --json flag - it means we can shorten example requests to something like:

curl http://localhost:8080/example.UserSession/ExpireTicket --json '{"user_id": "123", "ticket_id":"456"}'

Up to you if you want to replace all the occurrences; either way it's a copy-paste operation for the reader.

[slinkydeveloper]

@pcholakov I remember there was some concern with --json: #31