Remove duplicate cluster privilege for pipeline management

[jaymode]

During the development of version 5.0, two cluster level privileges were added for the management of pipelines manage_pipeline and manage_ingest_pipelines. manage_ingest_pipelines was added as part of monitoring during an attempt to future proof monitoring documents with the use of an ingest pipeline that was empty. manage_pipeline was added as part of a role for the add data feature in Kibana. The manage_pipeline name was the name chosen by the security team at that time and the manage_ingest_pipelines name was not reviewed by the security team.

My opinion is that the manage_ingest_pipelines name should be deprecated and removed in favor of the manage_pipeline name based on the history.

[elasticmachine]

Pinging @elastic/es-security (:Security/Authorization)

[jkakavas]

We discussed this in our team meeting today. We decided that it makes sense to keep one of the two privileges.

Short term actions:

• Remove manage_ingest_pipelines from the documentation
• Remove manage_ingest_pipelines from the response of Get builtin privileges

Tracked here

Mid term actions :

• Deprecate and remove the duplicate privilege. We believe that there should be a generic way to handle this kind of deprecation and we currently do not have one. This is not the first time such a need comes up and it won't be the last so I will ping @gwbrown discuss a possible plan.