Fixing import paths so generated headers work

The protobuf compiler uses the concept of a "canonical" path when
generating source files. This is the base point where it searches for
import files. It _expects_ that path will match the base path for
searching for headers, too. The end result is that

    import "v1/ustatus.proto"

will generate a C++ header that contains

    #include "v1/ustatus.pb.h"

while we have been explicitly asked to use includes starting with
`uprotocol` in up-cpp:

    #include "uprotocol/v1/ustatus.pb.h"

We were able to work around this with some tricks when the import paths
were file names only (e.g. `import ustatus.proto`). However, the proto
files have moved under the `v1/` directory as of #141.

Based on my reading of the protoc documentation and several stack
overflow postings, it seems the intended way for .proto files to be
written in this scenario is to import the full canonical path as
intended for the output files:

    import "uprotocol/v1/ustatus.proto"

so that protoc can generate the correct paths in output sources in the
first place.

up-core-api/uprotocol/core/udiscovery/v3/udiscovery.proto

@@ -15,9 +15,9 @@ syntax = "proto3";
 
 package uprotocol.core.udiscovery.v3;
 import "google/protobuf/timestamp.proto";
-import "uoptions.proto";
-import "v1/uri.proto";
-import "v1/ustatus.proto";
+import "uprotocol/uoptions.proto";
+import "uprotocol/v1/uri.proto";
+import "uprotocol/v1/ustatus.proto";
 
 option java_package = "org.eclipse.uprotocol.core.udiscovery.v3";
 option java_outer_classname = "UDiscoveryProto";

up-core-api/uprotocol/core/usubscription/v3/usubscription.proto

@@ -17,9 +17,9 @@ package uprotocol.core.usubscription.v3;
 
 import "google/protobuf/any.proto";
 import "google/protobuf/timestamp.proto";
-import "v1/ustatus.proto";
-import "v1/uri.proto";
-import "uoptions.proto";
+import "uprotocol/v1/ustatus.proto";
+import "uprotocol/v1/uri.proto";
+import "uprotocol/uoptions.proto";
 
 option java_package = "org.eclipse.uprotocol.core.usubscription.v3";
 option java_outer_classname = "USubscriptionProto";

up-core-api/uprotocol/core/utwin/v2/utwin.proto

@@ -15,10 +15,10 @@ syntax = "proto3";
 
 package uprotocol.core.utwin.v2;
 
-import "uoptions.proto";
-import "v1/ustatus.proto";
-import "v1/uri.proto";
-import "v1/umessage.proto";
+import "uprotocol/uoptions.proto";
+import "uprotocol/v1/ustatus.proto";
+import "uprotocol/v1/uri.proto";
+import "uprotocol/v1/umessage.proto";
 
 option java_package = "org.eclipse.uprotocol.core.utwin.v2";
 option java_outer_classname = "UTwinProto";

up-core-api/uprotocol/v1/uattributes.proto

@@ -15,10 +15,10 @@ syntax = "proto3";
 
 package uprotocol.v1;
 
-import "v1/uri.proto";
-import "v1/uuid.proto";
-import "v1/ustatus.proto";
-import "uoptions.proto";
+import "uprotocol/v1/uri.proto";
+import "uprotocol/v1/uuid.proto";
+import "uprotocol/v1/ustatus.proto";
+import "uprotocol/uoptions.proto";
 
 option java_package = "org.eclipse.uprotocol.v1";
 option java_outer_classname = "UAttributesProto";

up-core-api/uprotocol/v1/umessage.proto

@@ -15,7 +15,7 @@ syntax = "proto3";
 
 package uprotocol.v1;
 
-import "v1/uattributes.proto";
+import "uprotocol/v1/uattributes.proto";
 
 option java_package = "org.eclipse.uprotocol.v1";
 option java_outer_classname = "UMessageProto";