Migrate content from v5 "Queries, Search And Indexing"

[stevepiercy]

Links of affected pages in Plone Documentation, if any.

• https://6.docs.plone.org/backend/search.html

Description

Migrate content from Plone 5 docs.

• https://5.docs.plone.org/develop/plone/searching_and_indexing/index.html
• https://5.docs.plone.org/develop/plone/searching_and_indexing/catalog.html
• https://5.docs.plone.org/develop/plone/searching_and_indexing/query.html
• https://5.docs.plone.org/develop/plone/searching_and_indexing/external-catalogs.html
• https://5.docs.plone.org/develop/plone/searching_and_indexing/indexing.html
• https://5.docs.plone.org/external/plone.app.dexterity/docs/advanced/catalog-indexing-strategies.html

The last two need to be merged, as they contain duplicate information, but both have some information the other lacks.