[Canvas] Adds support for uppercase cluster names in esdocs and other datasource bug fixes

[cqliu1]

Summary

Closes #27099.
Closes #44135.
Closes #44141.

This fixes a few bugs surrounding default index patterns used in datasources, specifically in esdocs.

When initially visiting the Data tab to configure the datasource using Elasticsearch raw documents, the index argument in esdocs will be updated in the expression to the default index instead of leaving it out of the expression.

The 2nd fix resolves the error thrown by the Data tab when you navigate to it without having any default index pattern set by checking that a default index pattern exists before trying to retrieve the saved object from Elasticsearch.

The last fix adds support for uppercase cluster names by removing toLowerCase transforms on index names. Every instance of the index name was lowercased because Elasticsearch doesn't allow uppercase letters in the index names, but remote clusters do allow upper case letters in the cluster names.

To test support for case sensitive index names:

1. Install one of the sample data sets like kibana_sample_data_ecommerce.

2. Go into the Kibana dev console, and run this API call to create a remote cluster

PUT _cluster/settings
{
  "persistent": {
    "cluster": {
      "remote": {
        "cluster_ONE": {
          "seeds": [
            "127.0.0.1:9300"
          ]
        }
      }
    }
  }
}

3. Create an element that queries that index from the cluster_ONE remote cluster. Here's a sample expression:

filters
| esdocs index="cluster_ONE:kibana_sample_data_ecommerce" fields="taxful_total_price, user, order_date"
| alterColumn "order_date" name="Date Ordered"
| table
| render

4. If it works, the element should display data and not throw the error described in Canvas doesn't support upper case remote cluster names  #27099.

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

- [ ] This was checked for cross-browser compatibility, including a check against IE11
- [ ] Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
- [ ] Documentation was added for features that require explanation or tutorials
- [ ] Unit or functional tests were updated or added to match the most common scenarios
- [ ] This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-canvas

[ryankeairns]

I'm seeing the following error on step 3 when I 1) create the cluster then 2) add sample data:

When I reverse those steps and do 1) add sample data then 2) create the cluster then I see:

[spalger]

retest

[elasticmachine]

💔 Build Failed

• continuous-integration/kibana-ci/pull-request

[nik9000]

@elasticmachine run elasticsearch-ci/docs

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[clintandrewhall]

Nice set of fixes. LGTM.

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[ryankeairns]

Pulled down the latest, followed the steps, and successfully rendered the element!