Add common project

[lpatino10]

This PR adds a new common project with an SdkCommon class to handle logic that's common to the services, but doesn't belong in the core since it's project-specific. Currently, that means it handles building the User-Agent and X-IBMCloud-SDK-Analytics values that will be added to each service request.

This PR won't contain the changes to the service methods, but for reference, the code will look something like this:

public ServiceCall<QueryResponse> query(QueryOptions queryOptions) {
  ...
  RequestBuilder builder = RequestBuilder.post(RequestBuilder.constructHttpUrl(getEndPoint(), pathSegments, pathParameters));
  builder.query(VERSION, versionDate);
  if (queryOptions.loggingOptOut() != null) {
    builder.header("X-Watson-Logging-Opt-Out", queryOptions.loggingOptOut());
  }

  // Add any SDK-specific "default" headers.
  Map<String, String> defaultHeaders = SdkCommon.getDefaultHeaders("discovery", "v1", "query");
  for (Entry<String, String> header : defaultHeaders.entrySet()) {
    builder.header(header.getKey(), header.getValue());
  }
  ...
  final JsonObject contentJson = new JsonObject();
  ...
  builder.bodyJson(contentJson);
  return createServiceCall(builder.build(), ResponseConverterUtils.getObject(QueryResponse.class));
}

[lpatino10]

Leaving this as a draft until the core library is updated from this PR. Then, I'll update dependencies on this side to get everything working.

[padamstx]

technically speaking... :) the user agent header value could be stored in a static field and not computed each time getDefaultHeaders() is called. I'm sure the performance difference is negligible, but I couldn't stop myself from mentioning it :)

[lpatino10]

Any performance improvement is a good one! Done

[watson-github-bot]

🎉 This PR is included in version 7.0.0 🎉

The release is available on GitHub release

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