For #1158 - Use a dot instead of an underscore to seperate values

app/metrics.yaml

@@ -57,10 +57,10 @@ events:
       source:
         description: >
           A string that tells us how the user performed the search. Possible values are:
-          * default_action
-          * default_suggestion
-          * shortcut_action
-          * shortcut_suggestion
+          * default.action
+          * default.suggestion
+          * shortcut.action
+          * shortcut.suggestion
 
     bugs:
     - 959
@@ -327,7 +327,7 @@ metrics:
   search_count:
     type: labeled_counter
     description: >
-      The labels for this counter are `<search-engine-name>_<source>`.
+      The labels for this counter are `<search-engine-name>.<source>`.
 
       If the search engine is bundled with Fenix `search-engine-name` will be the name of the search engine. If it's a
       custom search engine (defined: https://github.com/mozilla-mobile/fenix/issues/1607) the value will be `custom`.

app/src/main/java/org/mozilla/fenix/components/metrics/Metrics.kt

@@ -14,6 +14,7 @@ import mozilla.components.support.base.log.logger.Logger
 import org.mozilla.fenix.BuildConfig
 import org.mozilla.fenix.R
 import java.lang.IllegalArgumentException
+import java.util.Locale
 
 sealed class Event {
 
@@ -171,10 +172,10 @@ sealed class Event {
                 }
 
             val countLabel: String
-                get() = "${source.searchEngine.name.toLowerCase()}_$label"
+                get() = "${source.searchEngine.name.toLowerCase(Locale.ROOT)}.$label"
 
             val sourceLabel: String
-                get() = "${source.descriptor}_$label"
+                get() = "${source.descriptor}.$label"
         }
 
         override val extras: Map<String, String>?