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 eclipse-uprotocol#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.

The generated code needs to be in the `uprotocol` namespace folder structure for clarity however the protos root was the uprotocol folder so generated code was missing the uprotocol folder. This change fixes the protos and cleans up the build to still work and validate the build/changes.

Applying suggestions from review.

This parameter should not be needed when pom.xml is in the current directory.

Co-authored-by: Steven Hartley <steven@orangepeel.ca>

The --file flag is not needed since pom.xml is in the repo root now.

The proto source root was also pointing to the wrong place now that the
xml file has been moved up a directory.

Also fixing the URLs for the project/repository since they were pointing
to the old core API archive.