FEATURE: Add search operator to see all direct messages from a user (#7913)

* FEATURE: Add search operator to see all direct messages from a user

* Only show message if related messages >= 5

* Make "all messages" the hyperlink

* Review

test/javascripts/acceptance/search-full-test.js.es6

@@ -278,7 +278,7 @@ QUnit.test(
 );
 
 QUnit.test(
-  "update in:private filter through advanced search ui",
+  "update in:personal filter through advanced search ui",
   async assert => {
     await visit("/search");
     await fillIn(".search-query", "none");
@@ -290,8 +290,8 @@ QUnit.test(
     );
     assert.equal(
       find(".search-query").val(),
-      "none in:private",
-      'has updated search term to "none in:private"'
+      "none in:personal",
+      'has updated search term to "none in:personal"'
     );
   }
 );