Create pre-configured EIS Kibana AI Connector for ESS and Serverless

[YulNaumenko]

EIS preconfigured connector should be defined for Serverless and ESS environments.

Implementation requires the changes in kibana-controller repository, similar to the kibanaPreconfiguredEmailSettings

https://github.com/elastic/kibana-controller/blob/76618b465561886e47b8e3cd7dd1105295b47995/internal/controllers/kibana/config/config_settings.go#L608-L625
We should follow the changes related to Elastic-Cloud-SMTP as an example.

To make it work for ESS we should update Cloud repository in a few places
similar to Elastic-Cloud-SMTP https://github.com/elastic/cloud/blob/23996e23f5c4adea28362f33117e37f5439f072e/scala-services/adminconsole/src/main/scala/no/found/adminconsole/api/v1/deployments/services/controlplanesettings/providers/kibana/KibanaDefaultSmtpConnectorSettings.scala#L52
and
https://github.com/elastic/cloud/blob/23996e23f5c4adea28362f33117e37f5439f072e/scala-services/constructor/src/test/scala/no/found/constructor/patchengine/KibanaSystemCredentialRotationTaskSpec.scala#L228

Kibana docs might also need to be updated

kibana/docs/management/connectors/pre-configured-connectors.asciidoc

Line 88 in 14c3235

* <<elasticcloud,`Elastic-Cloud-SMTP` preconfigured email connector>>