upstream discovery allow server name pass from request host

[yangboyd]

Please answer these questions before submitting a pull request, or your PR will get closed.

Why submit this pull request?

• [ ] Bugfix
• [x] New feature provided
• [ ] Improve performance
• [ ] Backport patches

What changes will this PR take into?

upstream discovery allow server name pass from request host add service_name_type field with value: pass, rewrite. The original service_name field is used as rewrite service name.

Please update this section with detailed description.

Related issues

fix/resolve #0001

Checklist:

• [x] Did you explain what problem does this PR solve? Or what new features have been added?
• [ ] Have you added corresponding test cases?
• [x] Have you modified the corresponding document?
• [x] Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[bzp2010]

Hi, @yangboyd.

I noticed that you updated schema.json and some Struct definitions which should not be modified manually, so I think this PR is inappropriate. If you need this feature, I'm afraid you'll have to do the entire data transformation on the front end instead of passing it to the back end.