[DOCS] Add "index template exists" API docs (#46095)

docs/reference/indices.asciidoc

@@ -45,6 +45,11 @@ index settings, aliases, mappings, and index templates.
 * <<indices-update-settings>>
 * <<indices-get-settings>>
 * <<indices-analyze>>
+
+[float]
+[[index-templates]]
+=== Index templates:
+* <<indices-template-exists>>
 * <<indices-templates>>
 
 [float]
@@ -109,6 +114,8 @@ include::indices/get-settings.asciidoc[]
 
 include::indices/analyze.asciidoc[]
 
+include::indices/template-exists.asciidoc[]
+
 include::indices/templates.asciidoc[]
 
 include::indices/stats.asciidoc[]

docs/reference/indices/template-exists.asciidoc

@@ -0,0 +1,56 @@
+[[indices-template-exists]]
+=== Index template exists API
+++++
+<titleabbrev>Index template exists</titleabbrev>
+++++
+
+Checks if an index template exists.
+
+
+
+[source,js]
+-----------------------------------------------
+HEAD /_template/template_1
+-----------------------------------------------
+// CONSOLE
+
+
+[[template-exists-api-request]]
+==== {api-request-title}
+
+`HEAD /_template/<index-template>`
+
+
+[[template-exists-api-desc]]
+==== {api-description-title}
+
+Use the index template exists API
+to determine whether one or more index templates exist.
+
+include::templates.asciidoc[tag=index-template-def]
+
+
+[[template-exists-api-path-params]]
+==== {api-path-parms-title}
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=index-template]
+
+
+[[template-exists-api-query-params]]
+==== {api-query-parms-title}
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=flat-settings]
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=local]
+
+include::{docdir}/rest-api/common-parms.asciidoc[tag=master-timeout]
+
+
+[[template-exists-api-response-codes]]
+==== {api-response-codes-title}
+
+`200`::
+Indicates all specified index templates exist.
+
+`404`::
+Indicates one or more specified index templates **do not** exist.

docs/reference/indices/templates.asciidoc

@@ -1,11 +1,12 @@
 [[indices-templates]]
 === Index Templates
 
-Index templates allow you to define templates that will automatically be
-applied when new indices are created. The templates include both 
-<<index-modules-settings,settings>> and <<mapping,mappings>>
-and a simple pattern template that controls whether the template should be 
-applied to the new index.
+// tag::index-template-def[]
+Index templates define <<index-modules-settings,settings>> and <<mapping,mappings>>
+that you can automatically apply when creating new indices.
+{es} applies templates to new indices
+based on an index pattern that matches the index name.
+// end::index-template-def[]
 
 NOTE: Templates are only applied at index creation time. Changing a template
 will have no impact on existing indices. When using the create index API, the
@@ -119,26 +120,6 @@ GET /_template
 --------------------------------------------------
 // CONSOLE
 
-[float]
-[[indices-templates-exists]]
-==== Template exists
-
-Used to check if the template exists or not. For example:
-
-[source,js]
------------------------------------------------
-HEAD _template/template_1
------------------------------------------------
-// CONSOLE
-
-The HTTP status code indicates if the template with the given name
-exists or not. Status code `200` means it exists and `404` means
-it does not.
-
-NOTE: Before 7.0.0, the 'mappings' definition used to include a type name. Although mappings
-no longer contain a type name by default, you can still use the old format by setting
-the parameter include_type_name. For more details, please see <<removal-of-types>>.
-
 [float]
 [[multiple-templates]]
 ==== Multiple Templates Matching

docs/reference/rest-api/common-parms.asciidoc

@@ -152,6 +152,13 @@ tag::index[]
 used to limit the request.
 end::index[]
 
+tag::index-template[]
+`<index-template>`::
+(Required, string)
+Comma-separated list or wildcard expression of index template names
+used to limit the request.
+end::index-template[]
+
 tag::lenient[]
 `lenient`::
 (Optional, boolean) If `true`, format-based query failures (such as