arrow

GH-37635: [Format][C++][Go] Add app_metadata to FlightInfo and FlightEndpoint (#37679)



### Rationale for this change
As suggested here: https://github.com/apache/arrow/issues/37635#issuecomment-1712146541 this just adds an `app_metadata` field to FlightInfo and FlightEndpoint

### What changes are included in this PR?
Just the updated proto file and the generated Go code from the proto

### Are there any user-facing changes?

Yes.

**This PR includes breaking changes to public APIs.**

* Closes: #37635

Lead-authored-by: Matt Topol <zotthewizard@gmail.com>
Co-authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Matt Topol <zotthewizard@gmail.com>