Fix 500 error on relase API for invalid tag_name

What does this MR do?

Fixes Issue #204718 (closed)

The fix is simple, Tags::CreateService#execute should return an error with http_status. Currently, since http_status is not passed to error() it takes HTTP status 500 as default. But, there are specs which expect 500 on invalid tag_name, not sure if it was intentional to return 500.

Also, Create Tags API always returns 400 on user input error, but if someone tries to create an existing tag name, it should ideally return 422? I need help in resolving this! 🤔

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