Add a fully-featured dashboard for Enterprise Search

[kovyrin]

What does this PR do?

This PR adds a fully-featured Kibana dashboard to be used with the new Enterprise Search module for metricbeat.
See the Screenshots section below for an example screenshot.

Why is it important?

Enterprise Search users need to be able to visualize the metrics produced by the new Enterprise Search metricbeat module. Since the Stack Monitoring integration is unlikely to land in 7.16 (elastic/kibana#114303), we want to ship the Kibana dashboard version of the same visualizations to make it easier to our users to consume new metrics in an efficient way.

Checklist

• My code follows the style guidelines of this project
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• Tested the new dashboard by importing it via the metricbeat setup command

How to test this PR locally

1. Go to x-pack/metricbeat
2. Build metricbeat via mage build
3. Import the dashboards:

./metricbeat setup --dashboards -E setup.dashboards.enabled=true -E setup.dashboards.always_kibana=true -E setup.kibana.host=http://localhost:5601/xtu -E setup.kibana.username=elastic -E setup.kibana.password=changeme -E setup.dashboards.directory=build/kibana -e -v

4. Run metricbeat with the enterprise search module against an Enterprise Search instance
5. Open Kibana and see some glorious graphs!

Screenshots

[mergify]

This pull request does not have a backport label. Could you fix it @kovyrin? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

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• Duration: 81 min 50 sec

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[sayden]

Linting failed, I guess it's the indentation of x-pack/metricbeat/module/enterprisesearch/module.yml. Try a mage fmt update

[kovyrin]

OK, CI tests pass and my local testing seems to work as well. What's the next step for getting this shipped? :-)

[richkuz]

I did a cursory review of the JSON file and looked at the screenshots. LGTM. 👍

I will wait for a proper build candidate and test it end-to-end after the merge.

[kovyrin]

For future reference: the file here was generated by the following command:

go run dev-tools/cmd/dashboards/export_dashboards.go -kibana http://elastic:changeme@localhost:5601 -yml x-pack/metricbeat/module/enterprisesearch/module.yml -folder x-pack/metricbeat/module/enterprisesearch