[DOCS] Document ingest processor description

[jrodewig]

Documents the processor-level description parameter added in #57906. Relates to #70442.

This PR covers the most visible places for setting up an ingest pipeline. I'll investigate adding additional processor-level descriptions as a separate effort.

cc @cjcenizal

Changes

• Adds the description parameter to the common parameters used on every processor docs page
• Adds usage examples to the ingest pipeline tutorials, create pipeline API docs, and enrich processor example

Previews

• Ingest pipeline tutorial: https://elasticsearch_70899.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/ingest.html
• Create pipeline API docs: https://elasticsearch_70899.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/put-pipeline-api.html
• Geo_match enrich processor example: https://elasticsearch_70899.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/geo-match-enrich-policy-type.html
• Match enrich processor example: https://elasticsearch_70899.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/match-enrich-policy-type.html
• Processor reference doc: https://elasticsearch_70899.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/append-processor.html

[elasticmachine]

Pinging @elastic/es-core-features (Team:Core/Features)

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[danhermann]

Thanks, @jrodewig. I left two minor comments below, neither of which are blocking.

[danhermann]

I might say something here about copying the value out of ingest metadata which is not indexed into the document so that the timestamp is indexed?

[danhermann]

Minor, but the processor description can be anything that's useful to the user and doesn't necessarily have to be about the processor's configuration.

[jrodewig]

I'll change this to:

Description of the processor. Useful for describing the purpose of the processor or its configuration.

[jrodewig]

Thanks @danhermann!