[DOCS] Add common scripting use cases with focus on runtime fields

[lockewritesdocs]

@elastic-jb created a document that outlines common scripting use cases with specific goals for each use case. Where applicable, we should use runtime fields to solve scripting goals. We should add a section for each of the following use cases under our docs for How to write scripts:

• Field extraction [[DOCS] Add field extraction use cases to scripting docs #71596]
• Date manipulation
• String manipulation
• Math
• Conversion
• Logic

[elasticmachine]

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

[elasticmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)