[Fleet] Implement logstash output form

[nchaulet]

Description

Related to #104987

In the effort to support logstash as a new output type we need to implement the output form and related APIs to do so.

The UI should:

• show the instructions to setup securely logstash with a new pipeline and API keys
• Allow the user to provide certificate for mutual TLS (certificates are required)

Instructions to setup Logstash

The instructions should allow the user to generate a secure API key for logstash with the privileges to write and auto create to logs-*, metrics-*, traces-* .logs-* datastream.

UI

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[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)