Fix URL handling on first load of PipelineRun or TaskRun

Avoid invalid / unexpected interim state when navigating back using
browser history by ensure we call `history.replace` instead of
`history.push` when we automatically update the URL to include the
selected task and/or step when rendering the PipelineRun or TaskRun
resource.

If the URL query params already specify a selected task and/or step
then push the new history entry into the stack as normal.

src/containers/PipelineRun/PipelineRun.js

@@ -221,7 +221,12 @@ export /* istanbul ignore next */ function PipelineRunContainer({ intl }) {
     }
 
     const browserURL = location.pathname.concat(`?${queryParams.toString()}`);
-    history.push(browserURL);
+    if (currentPipelineTaskName) {
+      history.push(browserURL);
+    } else {
+      // auto-selecting task & step on first load
+      history.replace(browserURL);
+    }
   }
 
   function cancel() {

src/containers/TaskRun/TaskRun.js

@@ -201,7 +201,12 @@ export function TaskRunContainer({ intl }) {
     }
 
     const browserURL = location.pathname.concat(`?${queryParams.toString()}`);
-    history.push(browserURL);
+    if (showTaskRunDetails || selectedStepId) {
+      history.push(browserURL);
+    } else {
+      // auto-selecting step on first load
+      history.replace(browserURL);
+    }
   }
 
   function cancel() {