Modify add sample data page object to verify that data actually got installed

[bhavyarm]

Kibana version: 8.0.0

Describe the bug:
This method needs to check that sample data actually got installed:

  async addSampleDataSet(id: string) {
      const isInstalled = await this.isSampleDataSetInstalled(id);
      if (!isInstalled) {
        await testSubjects.click(`addSampleDataSet${id}`);
        await this._waitForSampleDataLoadingAction(id);
      }
    }

[elasticmachine]

Pinging @elastic/kibana-qa (Team:QA)

[bhavyarm]

cc @flash1293 if you have thoughts on this. Thanks!

[flash1293]

If the http request installing sample data fails, an error toast is shown, so we could check for that. However, I'm not sure whether the request actually fails - maybe the Kibana server thinks everything's fine, but the data is not actually available in Elasticsearch.

[bhavyarm]

cc @dmlemeshko

[dmlemeshko]

I'm thinking if we should use API call to load sample data for the cases when we don't test loading as functionality. Request will go ok even if data already loaded. We just need to figure it out how to proceed, e.g. new service for API calls?

Relying on UI sounds like an overhead and not a reliable solution since we came to this issue.

[bhavyarm]

This issue came up because of this test failure - #82226. We are testing the UI Part where we install sample data. and in the after method we are removing the installed sample data.