[ResponseOps] Hyperlinks in Slack messages are broken when there is "…

…_" or "*" in the URL (elastic#170067)

Resolves elastic#165673

## Summary
`escapeSlack` function in the mustasche_renderer breakes the hyperlinks
by wrapping the URL with backticks.
So the below markdown template does not work.

`<{{context.alertDetailsUrl}}|View alert details>`

This PR removes the code that adds backticks. 
With this change action variables with text wrapped in asterisks
\*text\* will render as **text** or wrapped in underscores \_text\_ will
render as _text_ .


### 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


### To verify

- Create a slack connector
- Create a rule that uses a slack connector and use the above markdown
template
- Verify that hyperlink is working properly in slack

x-pack/plugins/actions/server/lib/mustache_renderer.test.ts

@@ -34,6 +34,7 @@ const variables = {
   ul: '_',
   st_lt: '*<',
   vl: '|',
+  link: 'https://te_st.com/',
 };
 
 describe('mustache_renderer', () => {
@@ -111,6 +112,7 @@ describe('mustache_renderer', () => {
       expect(renderMustacheString('{{ul}}', variables, 'slack')).toBe('`_`');
       // html escapes not needed when using backtic escaping
       expect(renderMustacheString('{{st_lt}}', variables, 'slack')).toBe('`*<`');
+      expect(renderMustacheString('{{link}}', variables, 'slack')).toBe('https://te_st.com/');
     });
 
     it('handles escape:json with commonly escaped strings', () => {

x-pack/plugins/actions/server/lib/mustache_renderer.ts

@@ -144,10 +144,14 @@ function escapeSlack(value: unknown): string {
   if (value == null) return '';
 
   const valueString = `${value}`;
-  // if the value contains * or _, escape the whole thing with back tics
+  // if the value contains * or _ and is not a url, escape the whole thing with back tics
   if (valueString.includes('_') || valueString.includes('*')) {
-    // replace unescapable back tics with single quote
-    return '`' + valueString.replace(/`/g, `'`) + '`';
+    try {
+      new URL(valueString);
+    } catch (e) {
+      // replace unescapable back tics with single quote
+      return '`' + valueString.replace(/`/g, `'`) + '`';
+    }
   }
 
   // otherwise, do "standard" escaping

x-pack/test/alerting_api_integration/common/plugins/alerts/server/alert_types.ts

@@ -28,6 +28,7 @@ export const EscapableStrings = {
   escapableHtml: '<&>',
   escapableDoubleQuote: '"double quote"',
   escapableLineFeed: 'line\x0afeed',
+  escapableLink: 'https://te_st.com/',
 };
 
 export const DeepContextVariables = {

x-pack/test/alerting_api_integration/spaces_only/tests/alerting/group4/mustache_templates.ts

@@ -84,7 +84,7 @@ export default function executionStatusAlertTests({ getService }: FtrProviderCon
         // from x-pack/test/alerting_api_integration/common/plugins/alerts/server/alert_types.ts,
         // const EscapableStrings
         const template =
-          '{{context.escapableBacktic}} -- {{context.escapableBold}} -- {{context.escapableBackticBold}} -- {{context.escapableHtml}}';
+          '{{context.escapableBacktic}} -- {{context.escapableBold}} -- {{context.escapableBackticBold}} -- {{context.escapableHtml}} -- {{context.escapableLink}}';
 
         const rule = await createRule({
           id: slackConnector.id,
@@ -95,7 +95,9 @@ export default function executionStatusAlertTests({ getService }: FtrProviderCon
         });
 
         const body = await retry.try(async () => waitForActionBody(slackSimulatorURL, rule.id));
-        expect(body).to.be("back'tic -- `*bold*` -- `'*bold*'` -- <&>");
+        expect(body).to.be(
+          "back'tic -- `*bold*` -- `'*bold*'` -- <&> -- https://te_st.com/"
+        );
       });
 
       it('should handle context variable object expansion', async () => {