Fixes Cypress flake by adding pipe, click, and should (elastic#92762)

## Summary

We were seeing flake tests with the error messages:

```ts
expected '<button.euiButton.euiButton--primary>' to have text 'Install 2 Elastic prebuilt rules ', but the text was 'Install 1 Elastic prebuilt rule '
```

Running this locally several times I was able to reproduce the flake. I was able to see that the click handler when clicked on the check boxes is not always taking effect for the first check box. A common issue with Cypress is that a lot of page loads and JS activities on pages can add/remove click handlers quickly such as when we are frosting and un-frosting a loading screen.

When we try and click on the click handlers for a test and the click handlers are not added yet, we miss one or more and end up with a flake test. Instead we can click as fast as possible using `pipe` and then checking that the check box is clicked before continuing using a `should`

Even though the loading screen is done frosting in these tests, the click handler can take one or two milliseconds before they end up being added to the checkboxes.

**Analysis**

When you have the flake and fail you can scroll in Cypress and pin a point in time and see that indeed we did not get the first checkbox checked even though we had a click. Which makes sense as within a few milliseconds the click handlers are added and we do check the second checkbox:
<img width="2083" alt="analysis" src="https://user-images.githubusercontent.com/1151048/109119992-a19d1b80-7702-11eb-882a-c035eba97455.png">

### Checklist

- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios

x-pack/plugins/security_solution/cypress/tasks/alerts_detection_rules.ts

@@ -116,9 +116,19 @@ export const reloadDeletedRules = () => {
   cy.get(RELOAD_PREBUILT_RULES_BTN).click({ force: true });
 };
 
+/**
+ * Selects the number of rules. Since there can be missing click handlers
+ * when the page loads at first, we use a pipe and a trigger of click
+ * on it and then check to ensure that it is checked before continuing
+ * with the tests.
+ * @param numberOfRules The number of rules to click/check
+ */
 export const selectNumberOfRules = (numberOfRules: number) => {
   for (let i = 0; i < numberOfRules; i++) {
-    cy.get(RULE_CHECKBOX).eq(i).click({ force: true });
+    cy.get(RULE_CHECKBOX)
+      .eq(i)
+      .pipe(($el) => $el.trigger('click'))
+      .should('be.checked');
   }
 };