[Serverless]: Clarify API key when using Logstash

[ppf2]

Serverless Docs

Elasticsearch

Description

It can be helpful to enhance this section: https://www.elastic.co/docs/current/serverless/elasticsearch/ingest-data-through-logstash#api-keys-for-connecting-ls-to-es3

To include a screenshot to direct customers to select the API key format for Logstash:

Some customers are attempting to use the base64 encoded form which is intended for REST API.

Even though we already have in-tool on-boarding for this on the Serverless Console, it can still be helpful to highlight this UI convenience feature to help them get the right format for the API Key for Logstash.

Additionally, since this helpful API key format feature is only available right after creating the API key from the UI (but not when managing existing API keys - an enhancement request we are discussing), we should also provide details on the expected API key format directly in the documentation. Specifically, Logstash expects the api_key to be in the format:

id:api_key

In order to construct the above format, the user will need to call GET API Key information API to obtain the id and then append their api_key value to it (https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-get-api-key.html)

While we do have the following example in the doc:

output {
  elasticsearch {
    api_key => "TiNAGG4BaaMdaH1tRfuU:KnR6yE41RrSowb0kQ0HWoA"
  }
}

It will be helpful to explain the format and how to construct it.

Resources and additional context

https://www.elastic.co/docs/current/serverless/elasticsearch/ingest-data-through-logstash#api-keys-for-connecting-ls-to-es3