[DOCS] [Roadmap] Add "Getting data into Elasticsearch" section

[jrodewig]

As part of our ongoing roadmap, we plan to add the following chapters to the Elasticsearch Reference Guide:

• Get data into Elasticsearch
  • Choose an ingest method
  • Configure data mappings
  • Analyze text strings

Tasks

• Rewrite Mapping to include API examples and tutorial. ([DOCS] Add examples to the mapping docs #45520)
• Add Field datatypes, Meta-Fields, and Mapping parameters to the Reference section
• Rewrite Analysis to include API examples and tutorial.
• Move conceptual and tutorial information from Ingest Nodes to the Choose an ingest method chapter
• Move conceptual and tutorial information from Mapping to the Configure data mappings chapter
• Move conceptual and tutorial information from Analysis to the Analyze text strings chapter
• Create Reference section
• Relocate Ingest APIs to REST APIs section ([DOCS] Relocate Ingest API docs to REST API section #45812)
• Add Processors to the Reference section
• Add Analyzers, Normalizers, Tokenizers, Token Filters, and Character Filters to the Reference section

FYI @debadair @wchrisdean

[elasticmachine]

Pinging @elastic/es-docs