fix: Per-model metrics disabled by default (#124)

PR #90 introduced support for per-model prometheus metrics with the
intention to not change the default behavior but require this as a feature
to be enabled explicitly via configuration. However, it was inadvertently
made the default.

This commit restores the original behavior by changing the default configuration
to not include modelId/vModelId prometheus metric labels because model-mesh
was designed primarily for use cases where there is a very large and changing
number of individual models and those scenarios would result in a much greater
number of individual metrics than prometheus can handle.

------

Signed-off-by: Nick Hill <nickhill@us.ibm.com>

src/main/java/com/ibm/watson/modelmesh/Metrics.java

@@ -172,7 +172,7 @@ public PrometheusMetrics(Map<String, String> params, Map<String, String> infoMet
             int port = 2112;
             boolean shortNames = true;
             boolean https = true;
-            boolean perModelMetricsEnabled = true;
+            boolean perModelMetricsEnabled = false;
             String memMetrics = "all"; // default to all
             for (Entry<String, String> ent : params.entrySet()) {
                 switch (ent.getKey()) {