Expose http headers to rpc calls context (#712)

CHANGELOG.md

apigrpc/apigrpc.swagger.json

go.mod

go.sum

server/api_event.go

server/api_rpc.go

server/pipeline_rpc.go

server/runtime.go

server/runtime_go.go

server/runtime_go_context.go

server/runtime_go_match_core.go

server/runtime_javascript.go

server/runtime_javascript_context.go

server/runtime_lua.go

server/runtime_lua_context.go

server/runtime_lua_nakama.go

vendor/github.com/heroiclabs/nakama-common/api/api.pb.go

.../github.com/heroiclabs/nakama-common/rtapi/realtime.pb.go

...or/github.com/heroiclabs/nakama-common/runtime/runtime.go

vendor/modules.txt